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1. The three hundred project: galaxy cluster mergers and their impact on the stellar component of brightest cluster galaxies

Author: Ana Contreras-Santos, Alexander Knebe, Frazer Pearce, Roan Haggar, Meghan Gray, Weiguang Cui, Gustavo Yepes, Marco De Petris, Federico De Luca, Chris Power, Robert Mostoghiu, Sebastián E Nuza, Matthias Hoeft, and UAM. Departamento de Física Teórica
Subjects: numerical [Methods], Cosmology and Nongalactic Astrophysics (astro-ph.CO), Large-Scale Structure of Universe, Cosmology: theory, Galaxies: clusters: general, Galaxies: haloes, Large-scale structure of Universe, Methods: numerical, haloes [Galaxies], Galaxies: Haloes, FOS: Physical sciences, Física, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, clusters: general [Galaxies], Astrophysics - Astrophysics of Galaxies, theory [Cosmology], Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Methods: Numerical, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Galaxy Astrophysics, Cosmology: Theory, Galaxies: Clusters: General, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: This is a pre-copyedited, author-produced PDF of an article accepted for publication in Monthly Notices of the Royal Astronomical Society following peer review. The version of recordMonthly Notices of the Royal Astronomical Society 511.2 (2022): 2897-2913 is available online at: https://academic.oup.com/mnras/article-abstract/511/2/2897/6517700?redirectedFrom=fulltext, Using the data set of the three hundred project, i.e. a suite of 324 hydrodynamical resimulations of cluster-sized haloes, we study galaxy cluster mergers and their effect on colour and luminosity changes of their brightest cluster galaxies (BCG). We track the main progenitor of each halo at z = 0 and search for merger situations based on its mass accretion history, defining mergers as very rapid increases in the halo mass. Based upon the evolution of the dynamical state of the cluster we define a pre-and post-merger phase. We create a list of all these events and statistically study their mass ratio and time-scales, with the former verifying that all instances are in fact major mergers. By comparing to a control sample of clusters without mergers, we study the effect mergers have on the stellar component of the BCG. Analysing the mass, age, and metallicity of the BCG stellar particles, we find that the stellar content of BCGs grows significantly during mergers and, even though the main growth mechanism is the accretion of older stars, there is even a burst in star formation induced by the merger. In our simulations, BCGs in mergers form in median around 70 per cent more stars than those normally growing, although this depends on the radius considered for defining the BCG. Regarding observable properties, we see an increase in SDSS-u luminosity of 20 per cent during mergers, accompanied by a slightly slower increase of the galaxy g-r colour as compared to the control sample
Published: 2022
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2. Pulsar Scintillation Studies with LOFAR: II. Dual-frequency scattering study of PSR J0826+2637 with LOFAR and NenuFAR

Author: Ziwei Wu, William A Coles, Joris P W Verbiest, Krishnakumar Moochickal Ambalappat, Caterina Tiburzi, Jean-Mathias Grießmeier, Robert A Main, Yulan Liu, Michael Kramer, Olaf Wucknitz, Nataliya Porayko, Stefan Osłowski, Ann-Sofie Bak Nielsen, Julian Y Donner, Matthias Hoeft, Marcus Brüggen, Christian Vocks, Ralf-Jürgen Dettmar, Gilles Theureau, Maciej Serylak, Vladislav Kondratiev, James W McKee, Golam M Shaifullah, Ihor P Kravtsov, Vyacheslav V Zakharenko, Oleg Ulyanov, Olexandr O Konovalenko, Philippe Zarka, Baptiste Cecconi, Léon V E Koopmans, Stéphane Corbel, Wu, Z, A Coles, W, W Verbiest, J, Moochickal Ambalappat, K, Tiburzi, C, Grie??meier, J, A Main, R, Liu, Y, Kramer, M, Wucknitz, O, Porayko, N, Os??owski, S, Bak Nielsen, A, Y Donner, J, Hoeft, M, Br??ggen, M, Vocks, C, Dettmar, R, Theureau, G, Serylak, M, Kondratiev, V, W McKee, J, Shaifullah, G, P Kravtsov, I, V Zakharenko, V, Ulyanov, O, O Konovalenko, O, Zarka, P, Cecconi, B, E Koopmans, L, Corbel, S, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Univers et Théories (LUTH (UMR_8102)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Observatoire de Paris - Site de Paris (OP), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE), ISM: cloud, Space and Planetary Science, pulsars: general, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], ISM: clouds, pulsars: individual: PSR J0826+2637
Abstract: Interstellar scattering (ISS) of radio pulsar emission can be used as a probe of the ionised interstellar medium (IISM) and causes corruptions in pulsar timing experiments. Two types of ISS phenomena (intensity scintillation and pulse broadening) are caused by electron density fluctuations on small scales (< 0.01 AU). Theory predicts that these are related, and both have been widely employed to study the properties of the IISM. Larger scales ($\sim$1-100\,AU) cause measurable changes in dispersion and these can be correlated with ISS observations to estimate the fluctuation spectrum over a very wide scale range. IISM measurements can often be modeled by a homogeneous power-law spatial spectrum of electron density with the Kolmogorov ($-11/3$) spectral exponent. Here we aim to test the validity of using the Kolmogorov exponent with PSR~J0826+2637. We do so using observations of intensity scintillation, pulse broadening and dispersion variations across a wide fractional bandwidth (20 -- 180\,MHz). We present that the frequency dependence of the intensity scintillation in the high frequency band matches the expectations of a Kolmogorov spectral exponent but the pulse broadening in the low frequency band does not change as rapidly as predicted with this assumption. We show that this behavior is due to an inhomogeneity in the scattering region, specifically that the scattering is dominated by a region of transverse size $\sim$40\,AU. The power spectrum of the electron density, however, maintains the Kolmogorov spectral exponent from spatial scales of 5$\times10^{-6}$\,AU to $\sim$100\,AU., Accepted for publication in MNRAS, typo fixed
Published: 2023
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3. Sub-arcsecond imaging with the International LOFAR Telescope I. Foundational calibration strategy and pipeline

Author: Martin J. Hardcastle, H. Paas, Matthias Hoeft, J. Moldon, R. Pizzo, Arthur Corstanje, A. Kappes, S. Mooney, John McKean, Gottfried Mann, Pietro Zucca, Harvey Butcher, M. Pandey-Pommier, Joseph R. Callingham, A. Nelles, S. Duscha, Marco Iacobelli, Aleksander Shulevski, V. N. Pandey, Ph. Zarka, Annalisa Bonafede, S. Badole, M. Ruiter, Ashish Asgekar, Hanna Rothkaehl, M. P. van Haarlem, P. Kukreti, Wolfgang Reich, Michel Tagger, J. M. Anderson, Marian Soida, A. H. W. M. Coolen, Judith H. Croston, Olaf Wucknitz, Neal Jackson, Heino Falcke, W. N. Brouw, Jochen Eislöffel, Philip Best, A. Drabent, F. Sweijen, F. de Gasperin, Dominik J. Schwarz, Cyril Tasse, J. B. R. Oonk, J. M. Griessmeier, Benedetta Ciardi, S. Damstra, A. J. van der Horst, Stefan J. Wijnholds, C. Groeneveld, E. Jütte, D. Engels, I. M. Avruch, Ralph A. M. J. Wijers, Léon V. E. Koopmans, Timothy W. Shimwell, Emanuela Orru, Andrzej Krankowski, R. J. van Weeren, Leah K. Morabito, A. W. Gunst, I. van Bemmel, D. Venkattu, Mark J. Bentum, Adam T. Deller, Christian Vocks, George K. Miley, John Conway, M. A. Garrett, M. Bondi, Matthias Kadler, E. Bonnassieux, H. J. A. Röttgering, API Other Research (FNWI), High Energy Astrophys. & Astropart. Phys (API, FNWI), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), European Commission, European Research Council, Ministerio de Ciencia e Innovación (España), Science and Technology Facilities Council (UK), Astronomy, and Kapteyn Astronomical Institute
Subjects: Astronomy, Pipeline (computing), active, Field of view, Astrophysics, 01 natural sciences, law.invention, high angular resolution, radiation mechanisms, law, galaxies, active, galaxies, 010303 astronomy & astrophysics, media_common, Physics, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Astrometry, Interferometry, Astrophysics - Instrumentation and Methods for Astrophysics, high angular resolution, jets, active [Galaxies], media_common.quotation_subject, galaxies: active, FOS: Physical sciences, Telescope, 0103 physical sciences, Calibration, Instrumentation and Methods for Astrophysics (astro-ph.IM), Remote sensing, non-thermal [Radiation mechanisms], non-thermal radiation, 010308 nuclear & particles physics, techniques: high angular resolution, active galaxies, Astronomy and Astrophysics, LOFAR, radiation mechanisms: non-thermal, galaxies: jets, Astrophysics - Astrophysics of Galaxies, high angular resolution [Techniques], non-thermal, radiation mechanisms, [SDU]Sciences of the Universe [physics], Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), non-thermal, galaxies, jets, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Astrophysics of Galaxies, jets [Galaxies], techniques, jets of galaxies
Abstract: Full list of authors: Morabito, L. K.; Jackson, N. J.; Mooney, S.; Sweijen, F.; Badole, S.; Kukreti, P.; Venkattu, D.; Groeneveld, C.; Kappes, A.; Bonnassieux, E.; Drabent, A.; Iacobelli, M.; Croston, J. H.; Best, P. N.; Bondi, M.; Callingham, J. R.; Conway, J. E.; Deller, A. T.; Hardcastle, M. J.; McKean, J. P.; Miley, G. K.; Moldon, J.; Röttgering, H. J. A.; Tasse, C.; Shimwell, T. W.; van Weeren, R. J.; Anderson, J. M.; Asgekar, A.; Avruch, I. M.; van Bemmel, I. M.; Bentum, M. J.; Bonafede, A.; Brouw, W. N.; Butcher, H. R.; Ciardi, B.; Corstanje, A.; Coolen, A.; Damstra, S.; de Gasperin, F.; Duscha, S.; Eislöffel, J.; Engels, D.; Falcke, H.; Garrett, M. A.; Griessmeier, J.; Gunst, A. W.; van Haarlem, M. P.; Hoeft, M.; van der Horst, A. J.; Jütte, E.; Kadler, M.; Koopmans, L. V. E.; Krankowski, A.; Mann, G.; Nelles, A.; Oonk, J. B. R.; Orru, E.; Paas, H.; Pandey, V. N.; Pizzo, R. F.; Pandey-Pommier, M.; Reich, W.; Rothkaehl, H.; Ruiter, M.; Schwarz, D. J.; Shulevski, A.; Soida, M.; Tagger, M.; Vocks, C.; Wijers, R. A. M. J.; Wijnholds, S. J.; Wucknitz, O.; Zarka, P.; Zucca, P., The International LOFAR Telescope is an interferometer with stations spread across Europe. With baselines of up to ~2000 km, LOFAR has the unique capability of achieving sub-arcsecond resolution at frequencies below 200 MHz. However, it is technically and logistically challenging to process LOFAR data at this resolution. To date only a handful of publications have exploited this capability. Here we present a calibration strategy that builds on previous high-resolution work with LOFAR. It is implemented in a pipeline using mostly dedicated LOFAR software tools and the same processing framework as the LOFAR Two-metre Sky Survey (LoTSS). We give an overview of the calibration strategy and discuss the special challenges inherent to enacting high-resolution imaging with LOFAR, and describe the pipeline, which is publicly available, in detail. We demonstrate the calibration strategy by using the pipeline on P205+55, a typical LoTSS pointing with an 8 h observation and 13 international stations. We perform in-field delay calibration, solution referencing to other calibrators in the field, self-calibration of these calibrators, and imaging of example directions of interest in the field. We find that for this specific field and these ionospheric conditions, dispersive delay solutions can be transferred between calibrators up to ~1.5° away, while phase solution transferral works well over ~1°. We also demonstrate a check of the astrometry and flux density scale with the in-field delay calibrator source. Imaging in 17 directions, we find the restoring beam is typically ~0.3′′ ×0.2′′ although this varies slightly over the entire 5 deg2 field of view. We find we can achieve ~80–300 μJy bm−1 image rms noise, which is dependent on the distance from the phase centre; typical values are ~90 μJy bm−1 for the 8 h observation with 48 MHz of bandwidth. Seventy percent of processed sources are detected, and from this we estimate that we should be able to image roughly 900 sources per LoTSS pointing. This equates to ~ 3 million sources in the northern sky, which LoTSS will entirely cover in the next several years. Future optimisation of the calibration strategy for efficient post-processing of LoTSS at high resolution makes this estimate a lower limit. © ESO 2022., This work made use of the Dutch national e-infrastructure with the support of the SURF Cooperative using grant no. EINF-262 LKM is grateful for support from the Medical Research Council (grant MR/T042842/1). S.M. acknowledges support from the Governmentof Ireland Postgraduate Scholarship Programme. E.B. acknowledges support from the ERC-ERG grant DRANOEL, n.714245. A.D. acknowledges support by the BMBF Verbundforschung under the grant 052020. J.H.C. acknowledges support from the UK Science and Technology Facilities Council (ST/R000794/1). P.N.B. is grateful for support from the UK STFC via grant ST/R000972/1. J.R.C. thanks the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) for support via the Talent Programme Veni grant. M.J.H. acknowledges support from the UK Science and Technology Facilities Council (ST/R000905/1). J.P.M. acknowledges support from the NetherlandsOrganization for Scientific Research (NWO, project number 629.001.023) and the Chinese Academy of Sciences (CAS, project number 114A11KYSB20170054). J.M. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísicade Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). R.J.v.W. acknowledges support from the ERC Starting Grant ClusterWeb 804208. D.J.S. acknowledges support by the GermanFederal Ministry for Science and Research BMBF-Verbundforschungsprojekt D-LOFAR 2.0 (grant numbers 05A20PB1). LOFAR (van Haarlem et al. 2013) is the Low Frequency Array designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland.
Published: 2022
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4. Sub-arcsecond imaging with the International LOFAR Telescope II. Completion of the LOFAR Long-Baseline Calibrator Survey

Author: G. K. Miley, Annalisa Bonafede, M. P. van Haarlem, Jochen Eislöffel, John McKean, P. C. G. van Dijk, M. A. Garrett, B. Ciardi, R. Blaauw, E. Jütte, Harvey Butcher, O. Wucknitz, Luitje Koopmans, Oleg Smirnov, M. Pandey-Pommier, Pietro Zucca, Joseph R. Callingham, S. Mooney, R. J. van Weeren, A. Nelles, Antonia Rowlinson, W. Reich, Heino Falcke, S. Duscha, Rajan Chhetri, Emanuela Orrú, G. Mann, Dominik J. Schwarz, Michiel A. Brentjens, P. Zarka, M. Ruiter, Hanna Rothkaehl, Kaspars Prūsis, Ralph A. M. J. Wijers, S. Badole, Jean-Mathias Griessmeier, P. Maat, Neal Jackson, Marco Iacobelli, Jeremy J. Harwood, Andrzej Krankowski, M. J. Norden, Vishambhar Pandey, A. J. van der Horst, John Morgan, F. Sweijen, Adam Deller, George Heald, S. Damstra, Martin J. Hardcastle, Mark J. Bentum, Ashish Asgekar, Leah K. Morabito, A. W. Gunst, M. Tagger, A. Shulevski, C. Vocks, A. Drabent, Javier Moldon, A. H. W. M. Coolen, M. Paas, Atvars Nikolajevs, W. N. Brouw, J. Sluman, Roberto Pizzo, Marcus Brüggen, Henk Mulder, Matthias Hoeft, F. de Gasperin, I. M. Avruch, J. A. Zensus, Arthur Corstanje, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique = Laboratory of Space Studies and Instrumentation in Astrophysics (LESIA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), European Commission, Ministerio de Ciencia e Innovación (España), Netherlands Organization for Scientific Research, UK Research and Innovation, Chinese Academy of Sciences, High Energy Astrophys. & Astropart. Phys (API, FNWI), Kapteyn Astronomical Institute, Center for Wireless Technology Eindhoven, and EM for Radio Science Lab
Subjects: active -Radio continuum, active [Galaxies], Radio galaxy, galaxies -Atmospheric physics, Astronomy, media_common.quotation_subject, FOS: Physical sciences, Flux, Murchison Widefield Array, ionosphere, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Surveys, Interplanetary scintillation, Instrumentation and Methods for Astrophysics (astro-ph.IM), Instrumentation, Remote sensing, media_common, Physics, Spectral index, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], Radio lines: galaxies, Astrophysics::Instrumentation and Methods for Astrophysics, interferometers [Instrumentation], Astronomy and Astrophysics, Quasar, LOFAR, Galaxies: active, interferometers -Techniques, Astrophysics - Astrophysics of Galaxies, galaxies [Radio lines], Space and Planetary Science, Sky, [SDU]Sciences of the Universe [physics], Instrumentation: interferometers, Astrophysics of Galaxies (astro-ph.GA), Techniques: interferometric, interferometric [Techniques], interferometric -Surveys -Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Full list of authors: Jackson, N.; Badole, S.; Morgan, J.; Chhetri, R.; Prūsis, K.; Nikolajevs, A.; Morabito, L.; Brentjens, M.; Sweijen, F.; Iacobelli, M.; Orrù, E.; Sluman, J.; Blaauw, R.; Mulder, H.; van Dijk, P.; Mooney, S.; Deller, A.; Moldon, J.; Callingham, J. R.; Harwood, J.; Hardcastle, M.; Heald, G.; Drabent, A.; McKean, J. P.; Asgekar, A.; Avruch, I. M.; Bentum, M. J.; Bonafede, A.; Brouw, W. N.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Coolen, A.; Corstanje, A.; Damstra, S.; Duscha, S.; Eislöffel, J.; Falcke, H.; Garrett, M.; de Gasperin, F.; Griessmeier, J. -M.; Gunst, A. W.; van Haarlem, M. P.; Hoeft, M.; van der Horst, A. J.; Jütte, E.; Koopmans, L. V. E.; Krankowski, A.; Maat, P.; Mann, G.; Miley, G. K.; Nelles, A.; Norden, M.; Paas, M.; Pandey, V. N.; Pandey-Pommier, M.; Pizzo, R. F.; Reich, W.; Rothkaehl, H.; Rowlinson, A.; Ruiter, M.; Shulevski, A.; Schwarz, D. J.; Smirnov, O.; Tagger, M.; Vocks, C.; van Weeren, R. J.; Wijers, R.; Wucknitz, O.; Zarka, P.; Zensus, J. A.; Zucca, P., The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In this paper, we present the complete survey, building on the preliminary analysis published in 2016 which covered approximately half the survey area. The final catalogue consists of 30 006 observations of 24 713 sources in the northern sky, selected for a combination of high low-frequency radio flux density and flat spectral index using existing surveys (WENSS, NVSS, VLSS, and MSSS). Approximately one calibrator per square degree, suitable for calibration of ≥200 km baselines is identified by the detection of compact flux density, for declinations north of 30° and away from the Galactic plane, with a considerably lower density south of this point due to relative difficulty in selecting flat-spectrum candidate sources in this area of the sky. The catalogue contains indicators of degree of correlated flux on baselines between the Dutch core and each of the international stations, involving a maximum baseline length of nearly 2000 km, for all of the observations. Use of the VLBA calibrator list, together with statistical arguments by comparison with flux densities from lower-resolution catalogues, allow us to establish a rough flux density scale for the LBCS observations, so that LBCS statistics can be used to estimate compact flux densities on scales between 300 mas and 2′′, for sources observed in the survey. The survey is used to estimate the phase coherence time of the ionosphere for the LOFAR international baselines, with median phase coherence times of about 2 min varying by a few tens of percent between theshortest and longest baselines. The LBCS can be used to assess the structures of point sources in lower-resolution surveys, with significant reductions in the degree of coherence in these sources on scales between 2′′ and 300 mas. The LBCS survey sources show a greater incidence of compact flux density in quasars than in radio galaxies, consistent with unified schemes of radio sources. Comparison with samples of sources from interplanetary scintillation (IPS) studies with the Murchison Widefield Array shows consistent patterns of detection of compact structure in sources observed both interferometrically with LOFAR and using IPS. © ESO 2022., Support for the operation of the MWA is provided by the Australian Government (NCRIS), under a contract to Curtin University administered by Astronomy Australia Limited. We acknowledge the Pawsey Supercomputing Centre which is supported by the Western Australian and Australian Governments. A.D. acknowledges support by the BMBF Verbundforschung under the grant 052020. L.K.M. is grateful for support from the UKRI Future Leaders Fellowship (grant MR/T042842/1). J. Moldón acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). J.P.M. acknowledges support from the Netherlands Organization for Scientific Research (NWO, project number 629.001.023) and the Chinese Academy of Sciences (CAS, project number 114A11KYSB20170054).
Published: 2022
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5. Modelling the Energy Spectra of Radio Relics

Author: Matthias Hoeft, Marcus Brüggen, and Denis Wittor
Subjects: Shock wave, Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), radio relics, cosmological simulations, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Compton scattering, FOS: Physical sciences, QB1-991, Astronomy and Astrophysics, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Radio spectrum, Radio telescope, galaxy clusters, intracluster medium, cosmic-ray energy spectra, adiabatic processes, Lagrangian tracer particles, Radio relics, Intracluster medium, Adiabatic process, Galaxy cluster, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics are diffuse synchrotron sources that illuminate shock waves in the intracluster medium. In recent years, radio telescopes have provided detailed observations about relics. Consequently, cosmological simulations of radio relics need to provide a similar amount of detail. In this methodological work, we include information on adiabatic compression and expansion, which have been neglected in the past in the modelling of relics. In a cosmological simulation of a merging galaxy cluster, we follow the energy spectra of shock accelerated cosmic-ray electrons using Lagrangian tracer particles. On board of each tracer particle, we compute the temporal evolution of the energy spectrum under the influence of synchrotron radiation, inverse Compton scattering, and adiabatic compression and expansion. Exploratory tests show that the total radio power and, hence, the integrated radio spectrum are not sensitive to the adiabatic processes. This is attributed to small changes in the compression ratio over time., 12 pages, 5 figure, accepted for publication in a special issue of Galaxies "A New Window on the Radio Emission from Galaxies, Galaxy Clusters and Cosmic Web: Current Status and Perspectives"
Published: 2021

6. Exploring the spectral properties of radio relics I: Integrated spectral index and Mach number

Author: Matthias Hoeft, Stefano Ettori, P Domínguez-Fernández, Franco Vazza, D. Wittor, K. Rajpurohit, Wittor, D, Ettori, S, Vazza, F, Rajpurohit, K, Hoeft, M, and Domínguez-Fernández, P
Subjects: Shock wave, shock wave, galaxies: clusters: intracluster medium, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio spectrum, methods: numerical, symbols.namesake, Radio relics, 0103 physical sciences, Surface brightness, 010303 astronomy & astrophysics, Galaxy cluster, Physics, Spectral index, Shock (fluid dynamics), 010308 nuclear & particles physics, Astronomy and Astrophysics, Mach number, galaxies: clusters: general, Space and Planetary Science, symbols, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics are the manifestation of electrons presumably being shock (re-)accelerated to high energies in the outskirts of galaxy clusters. However, estimates of the shocks' strength yield different results when measured with radio or X-ray observations. In general, Mach numbers obtained from radio observations are larger than the corresponding X-ray measurements. In this work, we investigate this Mach number discrepancy. For this purpose, we used the cosmological code ENZO to simulate a sample of galaxy clusters that host bright radio relics. For each relic, we computed the radio Mach number from the integrated radio spectrum and the X-ray Mach number from the X-ray surface brightness and temperature jumps. Our analysis suggests that the differences in the Mach number estimates follow from the way in which different observables are related to different parts of the underlying Mach number distribution: radio observations are more sensistive to the high Mach numbers present only in a small fraction of a shock's surface, while X-ray measurements reflect the average of the Mach number distribution. Moreover, X-ray measurements are very sensitive to the relic's orientation. If the same relic is observed from different sides, the measured X-ray Mach number varies significantly. On the other hand, the radio measurements are more robust, as they are unaffected by the relic's orientation., Comment: 20 pages, 15 figures, accepted for publication in MNRAS
Published: 2021
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7. Downstream depolarization in the Sausage Relic: a 1-4 GHz very large array study

Author: Matthias Hoeft, D. N. Hoang, Lawrence Rudnick, G. Di Gennaro, Andra Stroe, Dongsu Ryu, Christine Jones, H. J. A. Röttgering, William R. Forman, Marcus Brüggen, Ralph Kraft, Timothy W. Shimwell, R. J. van Weeren, Di Gennaro, G., van Weeren, R. J., Rudnick, L., Hoeft, M., Brüggen, M., Ryu, Dongsu, Röttgering, H. J. A., Forman, W., Stroe, A., Shimwell, T. W., Kraft, R. P., Jones, C., and Hoang, D. N.
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, Radio galaxy, Astrophysics - astrophysics of galaxies, Astrophysics - cosmology and nongalactic astrophysics, FOS: Physical sciences, Galaxy clusters, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Radio relics, Intracluster medium, 0103 physical sciences, Polarimetry, 584, 563, 1278, 858, 2086, 1261, Plasma astrophysics, Galactic and extragalactic astronomy, Anisotropy, 010303 astronomy & astrophysics, Shocks, Astrophysics::Galaxy Astrophysics, Galaxy cluster, 0105 earth and related environmental sciences, Physics, Center (category theory), Shock, Astronomy and Astrophysics, Polarization (waves), Magnetic field, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA)
Abstract: Radio relics are elongated sources related to shocks driven by galaxy cluster merger events. Although these objects are highly polarized at GHz frequencies ($\gtrsim 20\%$), high-resolution studies of their polarization properties are still lacking. We present the first high-resolution and high-sensitivity polarimetry study of the merging galaxy cluster CIZA J2242.8+5301 in the 1-4 GHz frequency band. We use the $QU$-fitting approach to model the Stokes $I$, $Q$ and $U$ emission, obtaining best-fit intrinsic polarization fraction ($p_0$), intrinsic polarization angle ($\chi_0$), Rotation Measure (RM) and wavelength-dependent depolarization ($\sigma_{\rm RM}$) maps of the cluster. Our analysis focuses on the northern relic (RN). For the first time in a radio relic, we observe a decreasing polarization fraction in the downstream region. Our findings are possibly explained by geometrical projections and/or by decreasing of the magnetic field anisotropy towards the cluster center. From the amount of depolarization of the only detected background radio galaxy, we estimate a turbulent magnetic field strength of $B_{\rm turb}\sim5.6~\mu$Gauss in the relic. Finally, we observe Rotation Measure fluctuations of about 30 rad m$^{-2}$ around at the median value of 140.8 rad m$^{-2}$ at the relic position., Comment: 26 pages, 23 Figures, 5 Tables. Accepted for publication in ApJ
Published: 2021

8. Physical insights from the spectrum of the radio halo in MACS J0717.5+3745

Author: Gianfranco Brunetti, Rossella Cassano, Matthias Hoeft, G. Di Gennaro, C. J. Riseley, Nicola Locatelli, Denis Wittor, A. Botteon, R. J. van Weeren, Timothy W. Shimwell, William R. Forman, A. Ignesti, Franco Vazza, M. Brienza, K. Rajpurohit, A. S. Rajpurohit, H. J. A. Röttgering, Marcus Brüggen, E. Bonnassieux, Annalisa Bonafede, A. Drabent, Rajpurohit K., Brunetti G., Bonafede A., Van Weeren R.J., Botteon A., Vazza F., Hoeft M., Riseley C.J., Bonnassieux E., Brienza M., Forman W.R., Rottgering H.J.A., Rajpurohit A.S., Locatelli N., Shimwell T.W., Cassano R., Di Gennaro G., Bruggen M., Wittor D., Drabent A., and Ignesti A.
Subjects: Acceleration of particles, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, Astrophysics - astrophysics of galaxies, Astrophysics - cosmology and nongalactic astrophysics, Inverse, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Intracluster medium, 0103 physical sciences, Surface brightness, Connection (algebraic framework), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, Spectral index, 010308 nuclear & particles physics, Astronomy and Astrophysics, Acceleration of particle, Turbulence, Magnetic field, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Magnetic fields, Galaxies: clusters: individual: MACS J0717.5+3745, Halo, Galaxies: clusters: general, Galaxies: clusters: intracluster medium, Energy (signal processing)
Abstract: We present new LOFAR observations of the massive merging galaxy cluster MACS J0717.5+3745. The cluster hosts the most powerful radio halo known to date. These new observations, in combination with published uGMRT (300$-$850 MHz) and VLA (1$-$6.5 GHz) data, reveal that the halo is more extended than previously thought, with a largest linear size of $\sim2.2 \rm Mpc$. The halo shows a steep spectrum ($\alpha_{144\,\text{MHz}}^{1.5\,\text{GHz}}\sim-1.4$) and a steepening ($\alpha_{1.5 \text{GHz}}^{5.5 \text{GHz}}\sim-1.9$) above 1.5 GHz. We find a strong scattering in spectral index maps on scales of 50$-$100 kpc. We suggest that such a strong scattering may be a consequence of the regime where inverse Compton dominate the energy losses of electrons. The spectral index becomes steeper and shows an increased curvature in the outermost regions of the halo. We combined the radio data with \textit{Chandra} observations to investigate the connection between the thermal and non-thermal components of the intracluster medium (ICM). Despite a significant substructure in the halo emission, the radio brightness correlates strongly with the X-ray brightness at all observed frequencies. The radio-versus-X-ray brightness correlation slope steepens at a higher radio frequency (from $b_{144 \text{MHz}}=0.67\pm0.05$ to $b_{3.0 \text{GHz}}=0.98\pm0.09$) and the spectral index shows a significant anti correlation with the X-ray brightness. Both pieces of evidence further support a spectral steepening in the external regions. The compelling evidence for a steep spectral index, the existence of a spectral break above 1.5 GHz, and the dependence of radio and X-ray surface brightness correlation on frequency are interpreted in the context of turbulent reacceleration models. Under this scenario, our results allowed us to constrain that the turbulent kinetic pressure of the ICM is up to 10%., Comment: 16 pages, 12 figures, accepted for publication in A&A
Published: 2021

9. A LOFAR-uGMRT spectral index study of distant radio halos

Author: Cyril Tasse, H. J. A. Röttgering, F. de Gasperin, R. J. van Weeren, A. Botteon, V. Cuciti, Gianfranco Brunetti, G. Di Gennaro, E. Osinga, Marcus Brüggen, Rossella Cassano, Matthias Hoeft, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), General, Intracluster Medium, Radiation Mechanisms, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Context (language use), Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Low frequency, 01 natural sciences, Spectral line, Clusters, 0103 physical sciences, General, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, Giant Metrewave Radio Telescope, Spectral index, Astrophysics of Galaxies, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Galaxies, Astrophysics - Astrophysics of Galaxies, Redshift, Non-Thermal, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Intracluster Medium, Cosmology and Nongalactic Astrophysics, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Context. Radio halos are megaparsec-scale diffuse radio sources{ mostly} located at the centres of merging galaxy clusters. The common mechanism invoked to explain their origin is the re-acceleration of relativistic particles caused by large-scale turbulence. Aims. Current re-acceleration models predict that a significant number of halos at high redshift should be characterised by very steep spectra ($\alpha, Comment: 23 pages, 22 figures, 4 tables; accepted for publication in A&A
Published: 2021
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10. Nonthermal phenomena in the center of Abell 1775

Author: R. J. van Weeren, Subhash C. Mandal, Simona Giacintucci, Mariachiara Rossetti, A. Botteon, Gianfranco Brunetti, F. de Gasperin, Cyril Tasse, Timothy W. Shimwell, H. J. A. Röttgering, Tiziana Venturi, Rossella Cassano, Matthias Hoeft, Fabio Gastaldello, V. Cuciti, Hiroki Akamatsu, Marcus Brüggen, A. Drabent, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Radiation mechanisms: non-thermal, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics - cosmology and nongalactic astrophysics, Astrophysics - astrophysics of galaxies, FOS: Physical sciences, Context (language use), Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Astrophysics - high energy astrophysical phenomena, Radio continuum: galaxies, 0103 physical sciences, Cluster (physics), Surface brightness, 010306 general physics, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astronomy and Astrophysics, LOFAR, Radiation mechanisms: thermal, Cold front, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), X-rays: galaxies: clusters, Galaxies: clusters: general, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Galaxies: clusters: intracluster medium
Abstract: Thermal gas in the center of galaxy clusters can show substantial motions that generate surface-brightness and temperature discontinuities known as cold fronts. The motions may be triggered by minor or off-axis mergers that preserve the cool core of the system. The dynamics of the thermal gas can also generate radio emission from the intra-cluster medium (ICM) and impact the evolution of clusters' radio sources. We aim to study the central region of Abell 1775, a system in an ambiguous dynamical state at $z=0.072$ which is known to host an extended head-tail radio galaxy, with the goal of investigating the connection between thermal and nonthermal components in its center. We made use of a deep (100 ks) Chandra observation accompanied by LOFAR 144 MHz, GMRT 235 MHz and 610 MHz, and VLA 1.4 GHz radio data. We find a spiral-like pattern in the X-ray surface brightness that is mirrored in the temperature and pseudo-entropy maps. Additionally, we characterize an arc-shaped cold front in the ICM. We interpret these features in the context of a slingshot gas tail scenario. The structure of the head-tail radio galaxy "breaks" at the position of the cold front, showing an extension that is detected only at low frequencies, likely due to its steep and curved spectrum. We speculate that particle reacceleration is occurring in the outer region of this tail, which in total covers a projected size of $\sim800$ kpc. We also report the discovery of revived fossil plasma with ultra-steep spectrum radio emission in the cluster core together with a central diffuse radio source that is bounded by the arc-shaped cold front. The results reported in this work demonstrate the interplay between thermal and nonthermal components in the cluster center and the presence of ongoing particle reacceleration in the ICM on different scales., 17 pages, 17 figures, 2 tables (including appendix); Updated to match the accepted version in A&A
Published: 2021
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11. Morphology of radio relics-II. Properties of polarized emission

Author: Andrea Mignone, W. E. Banda-Barragan, Denis Wittor, K. Rajpurohit, Franco Vazza, Bhargav Vaidya, Paola Domínguez-Fernández, Dipanjan Mukherjee, Matthias Hoeft, Marcus Brüggen, Dominguez-Fernandez P., Bruggen M., Vazza F., Hoeft M., Banda-Barragan W.E., Rajpurohit K., Wittor D., Mignone A., Mukherjee D., and Vaidya B.
Subjects: Shock wave, galaxies: clusters: intracluster medium, MHD, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Electron, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, methods: numerical, symbols.namesake, Radio relics, Intracluster medium, 0103 physical sciences, Faraday effect, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, acceleration of particle, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astronomy and Astrophysics, shock waves, Magnetic field, Shock (mechanics), Space and Planetary Science, symbols, intergalactic medium, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Radio relics are diffuse radio sources in galaxy clusters that are associated with merger shock waves. Detailed observations of radio relics in total intensity and in polarisation show complex structures on kiloparsec scales. The relation between the observed features and the underlying morphology of the magnetic field is not clear. Using three-dimensional magneto-hydrodynamical simulations, we study the polarised emission produced by a shock wave that propagates through a turbulent medium that resembles the intracluster medium. We model the polarised synchrotron emission on the basis of diffusive shock acceleration of cosmic-ray electrons. We find that the synchrotron emission produced in a shocked turbulent medium can reproduce some of the observed features in radio relics. Shock compression can give rise to a high polarisation fraction at the shock front and a partial alignment of the polarisation $E$-vectors with the shock normal. Our work confirms that radio relics can also be formed in an environment with a tangled magnetic field. We also discuss the effect of Faraday Rotation intrinsic to the source, and how our results depend on the angular resolution of observations., Accepted for publication in MNRAS, 22 pages, 23 figures
Published: 2021

12. The impact of solar wind variability on pulsar timing

Author: R.-J. Dettmar, Cees Bassa, Gottfried Mann, Caterina Tiburzi, J. Y. Donner, N. K. Porayko, E. van der Wateren, A.-S. Bak Nielsen, Pietro Zucca, Richard Fallows, Jean-Mathias Grießmeier, James M. Anderson, Marcus Brüggen, Christian Vocks, J. Künsemöller, Benedetta Ciardi, Matthias Hoeft, Evan Keane, Gemma H. Janssen, Stefan Oslowski, M. Serylak, G. Shaifullah, Michael Kramer, R. A. Main, Joris P. W. Verbiest, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Tiburzi, C, Shaifullah, G, Bassa, C, Zucca, P, Verbiest, J, Porayko, N, Van Der Wateren, E, Fallows, R, Main, R, Janssen, G, Anderson, J, Bak Nielsen, A, Donner, J, Keane, E, Kunsemoller, J, Oslowski, S, Griessmeier, J, Serylak, M, Bruggen, M, Ciardi, B, Dettmar, R, Hoeft, M, Kramer, M, Mann, G, and Vocks, C
Subjects: Astrophysics::High Energy Astrophysical Phenomena, Astronomy, FOS: Physical sciences, Context (language use), Astrophysics, 01 natural sciences, Spherical model, Pulsar, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, ISM: general, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, 010308 nuclear & particles physics, Gravitational wave, Astronomy and Astrophysics, LOFAR, Solar wind, Amplitude, solar wind, gravitational waves, 13. Climate action, Space and Planetary Science, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena, Radio wave
Abstract: High-precision pulsar timing requires accurate corrections for dispersive delays of radio waves, parametrized by the dispersion measure (DM), particularly if these delays are variable in time. In a previous paper we studied the Solar-wind (SW) models used in pulsar timing to mitigate the excess of DM annually induced by the SW, and found these to be insufficient for high-precision pulsar timing. Here we analyze additional pulsar datasets to further investigate which aspects of the SW models currently used in pulsar timing can be readily improved, and at what levels of timing precision SW mitigation is possible. Our goals are to verify: a) whether the data are better described by a spherical model of the SW with a time-variable amplitude rather than a time-invariant one as suggested in literature, b) whether a temporal trend of such a model's amplitudes can be detected. We use the pulsar-timing technique on low-frequency pulsar observations to estimate the DM and quantify how this value changes as the Earth moves around the Sun. Specifically, we monitor the DM in weekly to monthly observations of 14 pulsars taken with LOFAR across time spans of up to 6 years. We develop an informed algorithm to separate the interstellar variations in DM from those caused by the SW and demonstrate the functionality of this algorithm with extensive simulations. Assuming a spherically symmetric model for the SW density, we derive the amplitude of this model for each year of observations. We show that a spherical model with time-variable amplitude models the observations better than a spherical model with constant amplitude, but that both approaches leave significant SW induced delays uncorrected in a number of pulsars in the sample. The amplitude of the spherical model is found to be variable in time, as opposed to what has been previously suggested., 14 pages, 9 figures. Accepted for publication in Astronomy and Astrophysics
Published: 2021
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13. A perfect power-law spectrum even at the highest frequencies: the Toothbrush relic

Author: Matteo Murgia, M. Kierdorf, A. Drabent, Rainer Beck, Denis Wittor, Federica Govoni, C.J. Riseley, Franco Vazza, E. Bonnassieux, F. Loi, K. Rajpurohit, R. J. van Weeren, Matthias Hoeft, N. Locatelli, V. Vacca, Rajpurohit K., Vazza F., Hoeft M., Loi F., Beck R., Vacca V., Kierdorf M., Van Weeren R.J., Wittor D., Govoni F., Murgia M., Riseley C.J., Locatelli N., Drabent A., and Bonnassieux E.
Subjects: Physics, Spectral index, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Radiation mechanisms: non-thermal, 010308 nuclear & particles physics, Linear polarization, FOS: Physical sciences, Astronomy and Astrophysics, Astrophysics, Globular clusters: individual: 1RXS J0603.3+4213, Acceleration of particle, 01 natural sciences, Particle acceleration, Radio telescope, Radio relics, Orders of magnitude (time), Space and Planetary Science, Galaxies: magnetic field, Intracluster medium, 0103 physical sciences, Degree of polarization, 010303 astronomy & astrophysics, Galaxies: clusters: intracluster medium, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics trace shock fronts generated in the intracluster medium (ICM) during cluster mergers. The particle acceleration mechanism at the shock fronts is not yet completely understood. We observed the Toothbrush relic with the Effelsberg and Sardinia Radio Telescope at 14.25 GHz and 18.6 GHz, respectively. Unlike previously claimed, the integrated spectrum of the relic closely follows a power law over almost three orders of magnitude in frequency, with a spectral index of $\alpha_{\rm 58\,MHz}^{\rm 18.6\,GHz}=-1.16\pm0.03$. Our finding is consistent with a power-law injection spectrum, as predicted by diffusive shock acceleration theory. The result suggests that there is only little magnetic field strength evolution downstream to the shock. From the lack of spectral steepening, we find that either the Sunyaev-Zeldovich decrement produced by the pressure jump is less extended than $\sim$ 600\,kpc along the line of sight or, conversely, that the relic is located far behind in the cluster. For the first time, we detect linearly polarized emission from the "brush" at 18.6 GHz. Compared to 8.3 GHz, the degree of polarization across the brush increases at 18.6 GHz, suggesting a strong Faraday depolarization towards lower frequencies. The observed depolarization is consistent with an intervening magnetized screen that arise from the dense ICM containing turbulent magnetic fields. The depolarization, corresponding to a standard deviation of the Rotation Measures as high as $\sigma_{\rm RM}= 212\pm23\rm \,rad\,m^{-2}$, suggests that the brush is located in or behind the ICM. Our findings indicate that the Toothbrush can be consistently explained by the standard scenario for relic formation, Comment: Accepted for publication in A&A Letters
Published: 2020

14. The LOFAR Tied-Array all-sky survey: Timing of 21 pulsars including the first binary pulsar discovered with LOFAR

Author: V. I. Kondratiev, S. Sanidas, Benjamin Stappers, Olaf Wucknitz, C. M. Tan, Gottfried Mann, Daniele Michilli, Caterina Tiburzi, B. Ciardi, C. G. Bassa, Dominik J. Schwarz, C. Vocks, Matthias Hoeft, S. Cooper, Arpad Miskolczi, J.Y. Donner, Jason W. T. Hessels, J. van Leeuwen, Patrick Weltevrede, J.-M. Grießmeier, Michael Kramer, High Energy Astrophys. & Astropart. Phys (API, FNWI), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS)
Subjects: media_common.quotation_subject, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Binary number, Astrophysics, 01 natural sciences, Binary pulsar, law.invention, Telescope, Pulsar, law, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, media_common, High Energy Astrophysical Phenomena (astro-ph.HE), [PHYS]Physics [physics], Physics, Spectral index, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, White dwarf, Astronomy and Astrophysics, LOFAR, pulsars: individual: PSR J1658+3630, methods: data analysis, pulsars: PSR J1658+3630, Space and Planetary Science, Sky, methods: observational, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Abstract: We report on the multi-frequency timing observations of 21 pulsars discovered in the LOFAR Tied-Array All-Sky Survey (LOTAAS). The timing data were taken at central frequencies of 149 MHz (LOFAR) as well as 334 and 1532 MHz (Lovell Telecope). The sample of pulsars includes 20 isolated pulsars and the first binary pulsar discovered by the survey, PSR J1658$+$3630. We modelled the timing properties of the pulsars, which showed that they have, on average, larger characteristic ages. We present the pulse profiles of the pulsars across the three observing bands, where PSR J1643$+$1338 showed profile evolution that appears not to be well-described by the radius-to-frequency-mapping model. Furthermore, we modelled the spectra of the pulsars across the same observing bands, using a simple power law, and found an average spectral index of $-1.9 \pm 0.5$. Amongst the pulsars studied here, PSR J1657$+$3304 showed large flux density variations of a factor of 10 over 300 days, as well as mode changing and nulling on timescales of a few minutes. We modelled the rotational and orbital properties of PSR J1658$+$3630, which has a spin period of 33 ms in a binary orbit of 3.0 days with a companion of minimum mass of 0.87$M_{\odot}$, likely a Carbon-Oxygen or Oxygen-Neon-Magnesium type white dwarf. PSR J1658$+$3630 has a dispersion measure of 3.0 pc cm$^{-3}$, making it possibly one of the closest binary pulsars known., 21 pages, 12 figures, Accepted for publication in the Monthly Notices of the Royal Astronomical Society
Published: 2020
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15. The beautiful mess in Abell 2255

Author: F. de Gasperin, Gianfranco Brunetti, R. J. van Weeren, Martin J. Hardcastle, Rossella Cassano, Marco Iacobelli, G. Di Gennaro, Laura Birzan, Matthias Hoeft, Subhash C. Mandal, R. Pizzo, Daniele Dallacasa, Aurora Simionescu, Marcus Brüggen, Timothy W. Shimwell, A. Botteon, H. J. A. Röttgering, A. Drabent, Fabio Gastaldello, V. Cuciti, Annalisa Bonafede, Botteon A., Brunetti G., Van Weeren R.J., Shimwell T.W., Pizzo R.F., Cassano R., Iacobelli M., Gastaldello F., B rzan L., Bonafede A., Bruggen M., Cuciti V., Dallacasa D., De Gasperin F., Di Gennaro G., Drabent A., Hardcastle M.J., Hoeft M., Mandal S., Rottgering H.J.A., and Simionescu A.
Subjects: Non-thermal radiation sources, 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Abell cluster, Tailed radio galaxie, X-ray astronomy, 0103 physical sciences, Radio astronomy, Extragalactic radio source, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astronomy and Astrophysics, Galaxy cluster, Astrophysics - Astrophysics of Galaxies, Intracluster medium, Space and Planetary Science, Extended radiation source, Astrophysics of Galaxies (astro-ph.GA), Radio interferometry, Astrophysics - High Energy Astrophysical Phenomena, Classics
Abstract: We present LOFAR observations of one of the most spectacular objects in the radio sky: Abell 2255. This is a nearby ($z = 0.0806$) merging galaxy cluster hosting one of the first radio halos ever detected in the intra-cluster medium (ICM). The deep LOFAR images at 144 MHz of the central $\sim10$ Mpc$^2$ region show a plethora of emission on different scales, from tens of kpc to above Mpc sizes. In this work, we focus on the innermost region of the cluster. Among the numerous interesting features observed, we discover remarkable bright and filamentary structures embedded in the radio halo. We incorporate archival WSRT 1.2 GHz data to study the spectral properties of the diffuse synchrotron emission and find a very complex spectral index distribution in the halo spanning a wide range of values. We combine the radio data with Chandra observations to investigate the connection between the thermal and non-thermal components by quantitatively comparing the radio and X-ray surface brightness and the spectral index of the radio emission with the thermodynamical quantities of the ICM. Despite the multitude of structures observed in the radio halo, we find that the X-ray and radio emission are overall well correlated. The fact that the steepest spectrum emission is located in the cluster center and traces regions with high entropy possibly suggests the presence of seed particles injected by radio galaxies that are spread in the ICM by turbulence generating the extended radio halo., Comment: 17 pages, 13 figures, 4 tables (including appendix). Accepted for publication in ApJ
Published: 2020
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16. Dispersion measure variability for 36 millisecond pulsars at 150 MHz with LOFAR

Author: Rene P. Breton, C. Vocks, A. V. Bilous, Stefan Oslowski, J. Y. Donner, J. Künsemöller, Michael Kramer, A.-S. Bak Nielsen, Evan Keane, James M. Anderson, V. I. Kondratiev, M. Serylak, Caterina Tiburzi, B. Ciardi, O. Wucknitz, Marcus Brüggen, Charlotte Sobey, J. van Leeuwen, J. W. McKee, Joris P. W. Verbiest, Matthias Hoeft, J.-M. Grießmeier, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), CNRS-INSU, and European Project: 617199,EC:FP7:ERC,ERC-2013-CoG,ALERT(2014)
Subjects: ISM: structure, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, law.invention, Telescope, Pulsar, Millisecond pulsar, law, pulsars: general, 0103 physical sciences, Dispersion (optics), 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [PHYS]Physics [physics], 010308 nuclear & particles physics, Gravitational wave, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, gravitational waves, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), ddc:520, Radio frequency, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Noise (radio)
Abstract: Radio pulses from pulsars are affected by plasma dispersion, which results in a frequency-dependent propagation delay. Variations in the magnitude of this effect lead to an additional source of red noise in pulsar timing experiments, including pulsar timing arrays that aim to detect nanohertz gravitational waves. We aim to quantify the time-variable dispersion with much improved precision and characterise the spectrum of these variations. We use the pulsar timing technique to obtain highly precise dispersion measure (DM) time series. Our dataset consists of observations of 36 millisecond pulsars, which were observed for up to 7.1 years with the LOFAR telescope at a centre frequency of ~150 MHz. Seventeen of these sources were observed with a weekly cadence, while the rest were observed at monthly cadence. We achieve a median DM precision of the order of 10^-5 cm^-3 pc for a significant fraction of our sources. We detect significant variations of the DM in all pulsars with a median DM uncertainty of less than 2x10^-4 cm^-3 pc. The noise contribution to pulsar timing experiments at higher frequencies is calculated to be at a level of 0.1-10 us at 1.4 GHz over a timespan of a few years, which is in many cases larger than the typical timing precision of 1 us or better that PTAs aim for. We found no evidence for a dependence of DM on radio frequency for any of the sources in our sample. The DM time series we obtained using LOFAR could in principle be used to correct higher-frequency data for the variations of the dispersive delay. However, there is currently the practical restriction that pulsars tend to provide either highly precise times of arrival (ToAs) at 1.4 GHz or a high DM precision at low frequencies, but not both, due to spectral properties. Combining the higher-frequency ToAs with those from LOFAR to measure the infinite-frequency ToA and DM would improve the result., Comment: 16 pages, 8 figures, 2 tables
Published: 2020
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17. A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances

Author: M. Iacobelli, M. A. Garrett, I. Max Avruch, Bartosz Dabrowski, Hanna Rothkaehl, Richard Fallows, Michiel van Haarlem, Olaf Wucknitz, A. W. Gunst, Tom Allbrook, Jean Matthias Grießmeier, Harvey Butcher, Christian Vocks, Jörg R. Hörandel, Vishambhar Pandey, Léon V. E. Koopmans, Anna Nelles, Biagio Forte, Barbara Matyjasiak, P. Maat, Gareth Dorrian, Thomas M. O. Franzen, M. Ruiter, Ashish Asgekar, Oleg Smirnov, Ilse van Bemmel, Antonia Rowlinson, Matthijs H. D. van der Wiel, M. Serylak, Ivan Astin, Dominik J. Schwarz, Mark J. Bentum, Arnold van Ardenne, Matthias Hoeft, Gottfried Mann, S. Duscha, Alex Arnold, Huib Intema, H. Paas, S. Damstra, Francesco de Gasperin, James M. Anderson, Jochen Eislöffel, Maaijke Mevius, Benedetta Ciardi, Andrzej Krankowski, M. Carmen Toribio, Alan Wood, Satyendra Thoudam, Aleksander Shulevski, Mario M. Bisi, Ralph A. M. J. Wijers, Pietro Zucca, Philippe Zarka, Wolfgang Reich, Marian Soida, Rene C. Vermeulen, Matthias Steinmetz, Netherlands Institute for Radio Astronomy (ASTRON), Environmental Systems Science Centre [Reading] (ESSC), University of Reading (UOR), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Department of Computer Science [Chapel Hill], University of North Carolina [Chapel Hill] (UNC), University of North Carolina System (UNC)-University of North Carolina System (UNC), Eindhoven Technical University, STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Thüringer Landessternwarte Tautenburg (TLS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), SKA South Africa, Ska South Africa, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), and Astronomy
Subjects: Atmospheric Science, 010504 meteorology & atmospheric sciences, Astronomy, FOS: Physical sciences, Instability mechanisms, lcsh:QC851-999, 01 natural sciences, Physics::Geophysics, Physics - Geophysics, travelling ionospheric disturbances, Interplanetary scintillation, Physics - Space Physics, Ionospheric scintillation, 0103 physical sciences, ddc:550, Gravity wave, Travelling ionospheric disturbances, 010303 astronomy & astrophysics, Physics::Atmospheric and Oceanic Physics, 0105 earth and related environmental sciences, Physics, [PHYS]Physics [physics], Earth and Planetary Astrophysics (astro-ph.EP), Scintillation, Scattering, LOFAR, Geodesy, Space Physics (physics.space-ph), Geophysics (physics.geo-ph), instability mechanisms, Earth's magnetic field, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Physics::Space Physics, lcsh:Meteorology. Climatology, Ionosphere, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Ionosonde, Astrophysics - Earth and Planetary Astrophysics
Abstract: This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cas A, taken overnight on 18-19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10-80MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR "core" reveals two different velocities in the scintillation pattern: a primary velocity of ~30m/s with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110m/s with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller--scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported., Comment: 24 pages, 16 figures. Accepted for open-access publication in the Journal of Space Weather and Space Climate. For associated movie file, see https://www.swsc-journal.org/10.1051/swsc/2020010/olm
Published: 2020
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18. Fast magnetic field amplification in distant galaxyclusters

Author: Huub Röttgering, S. Mandal, Marcus Brüggen, Mariachiara Rossetti, Gianfranco Brunetti, Annalisa Bonafede, Gabriella Di Gennaro, Rossella Cassano, Reinout J. van Weeren, A. Botteon, Matthias Hoeft, Timothy W. Shimwell, Aurora Simionescu, Daniele Dallacasa, Paola Domínguez-Fernández, Francesco de Gasperin, Torsten A. Enßlin, V. Cuciti, Fabio Gastaldello, Di Gennaro G., van Weeren R.J., Brunetti G., Cassano R., Bruggen M., Hoeft M., Shimwell T.W., Rottgering H.J.A., Bonafede A., Botteon A., Cuciti V., Dallacasa D., de Gasperin F., Dominguez-Fernandez P., Ensslin T.A., Gastaldello F., Mandal S., Rossetti M., and Simionescu A.
Subjects: Active galactic nucleus, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio spectrum, symbols.namesake, 0103 physical sciences, Faraday effect, Astrophysics - Cosmology and Nongalactic Astrophysic, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astronomy and Astrophysics, LOFAR, Galaxy, Redshift, Magnetic field, symbols, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: In the present-day Universe, magnetic fields pervade galaxy clusters, with strengths of a few microGauss obtained from Faraday Rotation. Evidence for cluster magnetic fields is also provided by Megaparsec-scale radio emission, namely radio halos and relics. These are commonly found in merging systems and are characterized by a steep radio spectrum. It is widely believed that magneto-hydrodynamical turbulence and shock-waves (re-)accelerate cosmic rays, producing halos and relics. The origin and the amplification of magnetic fields in clusters is not well understood. It has been proposed that turbulence drives a small-scaledynamo that amplifies seed magnetic fields (primordial and/or injected by galactic outflows, as active galactic nuclei, starbursts, or winds). At high redshift, radio halos are expected to be faint, due to the Inverse Compton losses and dimming effect with distance. Moreover, Faraday Rotation measurements are difficult to obtain. If detected, distant radio halosprovide an alternative tool to investigate magnetic field amplification. Here, we report LOFAR observations which reveal diffuse radio emission in massive clusters when the Universe was only half of its present age, with a sample occurrence fraction of about 50%. The high radio luminosities indicate that these clusters have similar magnetic field strengths to those in nearby clusters, and suggest that magnetic field amplification is fast during the first phases ofcluster formation., Comment: Published in Nature Astronomy on 2 November 2020. The published version is available at this URL https://www.nature.com/articles/s41550-020-01244-5#citeas
Published: 2020
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19. LOFAR 144-MHz follow-up observations of GW170817

Author: Oleg Smirnov, Martin J. Hardcastle, P. Zarka, Adam Stewart, H. Paas, D. Carbone, P. Maat, Dominik J. Schwarz, M. C. Toribio, David A. Nichols, G. Mann, Rudy Wijnands, A. J. van der Horst, Evan Keane, H. J. A. Röttgering, Olaf Wucknitz, C. Tasse, T. Muñoz-Darias, Henk Mulder, M. H. D. van der Wiel, Kenta Hotokezaka, M. P. van Haarlem, Stephane Corbel, J. B. R. Oonk, S. ter Veen, A. W. Gunst, W. N. Brouw, Casey J. Law, M. Iacobelli, K. Gourdji, Samaya Nissanke, J. W. Broderick, Timothy W. Shimwell, R. Pekal, Rob Fender, W. Reich, James M. Anderson, Matthias Hoeft, Anna Nelles, R. Blaauw, Luitje Koopmans, J. van Leeuwen, Aleksandar Shulevski, R. J. van Weeren, Pietro Zucca, Marian Soida, Martin Bell, Ralph A. M. J. Wijers, Vanessa A. Moss, M. Pandey-Pommier, Thomas M. O. Franzen, Antonia Rowlinson, Anjali A. A. Piette, S. Duscha, Richard Fallows, M. A. Garrett, Peter G. Jonker, Mark J. Bentum, J.-M. Grießmeier, M. de Vos, B. Ciardi, Jörg R. Hörandel, E. Jütte, C. Vocks, M. Serylak, Andrzej Krankowski, Marcus Brüggen, Jochen Eislöffel, M. Pietka, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), High Energy Astrophys. & Astropart. Phys (API, FNWI), Astroparticle Physics (IHEF, IoP, FNWI), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Laboratoire de physique et chimie de l'environnement (LPCE), Université d'Orléans (UO)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Astronomy, and Kapteyn Astronomical Institute
Subjects: Astronomy, FOS: Physical sciences, Binary number, Astrophysics, Astronomy & Astrophysics, 01 natural sciences, Radio spectrum, stars: neutron, neutron [stars], 0201 Astronomical and Space Sciences, 0103 physical sciences, 14. Life underwater, Center frequency, 010306 general physics, stars [radio continuum], 010303 astronomy & astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, [PHYS]Physics [physics], Spectral index, Gravitational wave, Astronomy and Astrophysics, LOFAR, Afterglow, Neutron star, gravitational waves, Space and Planetary Science, ddc:520, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], radio continuum: stars
Abstract: We present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO-Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13.7 degrees when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130-138 and 371-374 days after the merger event, we obtain 3$\sigma$ upper limits for the afterglow component of 6.6 and 19.5 mJy beam$^{-1}$, respectively. Using our best upper limit and previously published, contemporaneous higher-frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index $\alpha^{610}_{144} \gtrsim -2.5$. We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations., Comment: 9 pages, 2 figures, accepted for publication in MNRAS
Published: 2020
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20. Testing the accuracy of the ionospheric Faraday rotation corrections through LOFAR observations of bright northern pulsars

Author: M. Serylak, Michael Kramer, Marcus Brüggen, A. Horneffer, James M. Anderson, A. Noutsos, J. Künsemöller, Olaf Wucknitz, Dominik J. Schwarz, Caterina Tiburzi, Dominic Schnitzeler, N. K. Porayko, Stefan Oslowski, Joris P. W. Verbiest, Matthias Hoeft, J.-M. Grießmeier, Max-Planck-Institut für Radioastronomie (MPIFR), Universität Bielefeld, Swinburne University of Technology [Melbourne], University of Hamburg, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)
Subjects: Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, 01 natural sciences, Physics::Geophysics, stars: neutron, symbols.namesake, Pulsar, pulsars: general, 0103 physical sciences, Faraday effect, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, [PHYS]Physics [physics], Physics, polarization, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Polarization (waves), Magnetic field, Earth's magnetic field, Space and Planetary Science, Physics::Space Physics, symbols, Ionosphere, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - Instrumentation and Methods for Astrophysics, Interplanetary spaceflight, atmospheric effects
Abstract: Faraday rotation of polarized emission from pulsars measured at radio frequencies provides a powerful tool to investigate the interstellar and interplanetary magnetic fields. However, besides being sensitive to the astrophysical media, pulsar observations in radio are affected by the highly time-variable ionosphere. In this article, the amount of ionospheric Faraday rotation has been computed by assuming a thin layer model. For this aim, ionospheric maps of the free electron density (based on Global Positioning System data) and semi-empirical geomagnetic models are needed. Through the data of five highly polarized pulsars observed with the individual German LOw-Frequency ARray stations, we investigate the performances of the ionospheric modelling. In addition, we estimate the parameters of the systematics and the correlated noise generated by the residual unmodelled ionospheric effects, and show the comparison of the different free-electron density maps. For the best ionospheric maps, we have found that the rotation measure corrections on one-year timescales after subtraction of diurnal periodicity are accurate to $\sim$ 0.06--0.07 rad m$^{-2}$., 18 pages, 13 figures, 4 tables
Published: 2018
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21. First evidence of diffuse ultra-steep-spectrum radio emission surrounding the cool core of a cluster

Author: A. Wilber, A. Botteon, D. Rafferty, Timothy W. Shimwell, Annalisa Bonafede, G. Brunetti, H. J. A. Röttgering, Marcus Brüggen, V. Cuciti, Huib Intema, F. Savini, Glenn J. White, R. J. van Weeren, Matthias Hoeft, Rossella Cassano, Simona Giacintucci, F. de Gasperin, Savini, F., Bonafede, A., Brüggen, M., van Weeren, R., Brunetti, G., Intema, H., Botteon, A., Shimwell, T., Wilber, A., Rafferty, D., Giacintucci, S., Cassano, R., Cuciti, V., de Gasperin, F., Röttgering, H., Hoeft, M., and White, G.
Subjects: Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Electron, Astrophysics, 01 natural sciences, law.invention, law, 0103 physical sciences, Cluster (physics), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Physics, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Synchrotron, Particle acceleration, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Galaxies: clusters: individual: PSZ1G139.61+24.20, Halo
Abstract: Diffuse synchrotron radio emission from cosmic ray electrons is observed at the centre of a number of galaxy clusters. These sources can be classified either as giant radio haloes, which occur in merging clusters, or as mini haloes, which are found only in cool-core clusters. In this paper, we present the first discovery of a cool-core cluster with an associated mini halo that also shows ultra-steep-spectrum emission extending well beyond the core that resembles radio halo emission. The large-scale component is discovered thanks to LOFAR observations at 144 MHz. We also analyse GMRT observations at 610 MHz to characterize the spectrum of the radio emission. An X-ray analysis reveals that the cluster is slightly disturbed, and we suggest that the steep-spectrum radio emission outside the core could be produced by a minor merger that powers electron re-acceleration without disrupting the cool core. This discovery suggests that, under particular circumstances, both a mini halo and giant halo could co-exist in a single cluster, opening new perspectives for particle acceleration mechanisms in galaxy clusters.
Published: 2018
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22. No Pulsar Companion Around the Nearest Low Mass White Dwarf

Author: Tilemachos M. Athanasiadis, Nataliya K. Porayko, John Antoniadis, David Champion, Olaf Wucknitz, Benedetta Ciardi, Matthias Hoeft, and Michael Kramer
Subjects: Astrophysics - Solar and Stellar Astrophysics, Astrophysics::High Energy Astrophysical Phenomena, Astrophysics::Instrumentation and Methods for Astrophysics, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, General Medicine, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract: 2MASS J050051.85$-$093054.9 is the closest known low-mass helium-core white dwarf in a binary system. We used three high-band international LOFAR stations to perform a targeted search for a pulsar companion, reaching sensitivities of ~3 mJy for a 10-ms pulsar at a DM = 1 pc$\cdot$cm$^{-3}$. No pulsed signal was detected, confidently excluding the presence of a detectable radio pulsar in the system., Accepted for publication in the Research Notes of the AAS
Published: 2021
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23. Abell 1430: A merging cluster with exceptional diffuse radio emission

Author: Mariachiara Rossetti, K. Rajpurohit, Fabio Gastaldello, Rossella Cassano, Gianfranco Brunetti, Matthias Hoeft, R. J. van Weeren, F. Andrade-Santos, Sebastián E. Nuza, Timothy W. Shimwell, H. J. A. Röttgering, H. Meusinger, Gustavo Yepes, C. Dumba, A. Drabent, Lorenzo Lovisari, Marcus Brüggen, Dominique Eckert, and A. Botteon
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Interferometric, Radio Continuum, Astrophysics::High Energy Astrophysical Phenomena, Radiation Mechanisms, FOS: Physical sciences, Individual, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Luminosity, Clusters, Jansky, Thermal, X-rays, 0103 physical sciences, General, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Spectral index, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Galaxies, Techniques, Galaxy, Non-Thermal, Radio halo, Space and Planetary Science, Halo, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Diffuse radio emission has been found in many galaxy clusters, predominantly in massive systems which are in the state of merging. The radio emission can usually be classified as relic or halo emission, which are believed to be related to merger shocks or volume-filling turbulence, respectively. Recent observations have revealed radio bridges for some pairs of very closeby galaxy clusters. The mechanisms that may allow to explain the high specific density of relativistic electrons, necessary to explain the radio luminosity of these bridge regions, are poorly explored. We analyse the galaxy cluster Abell 1430 with LoTSS data in detail and complement it with recent JVLA L-band observations, XMM-Newton, Chandra, and SDSS data. Moreover, we compare our results to clusters extracted from the "The Three Hundred Project" cosmological simulation. We find that Abell 1430 consists of two components, namely A1430-A and A1430-B. We speculate that the two components undergo an off-axis merger. The more massive component shows diffuse radio emission which can be classified as radio halo showing a low radio power given the mass of the cluster. Most interestingly, there is extended diffuse radio emission, dubbed as the `Pillow', which is apparently related to A1430-B and thus related to low density intracluster or intergalactic medium. To date, a only few examples for emission originating from such regions are known. These discoveries are crucial to constrain possible acceleration mechanisms, which may allow to explain the presence of relativistic electrons in these regions. Our results indicate a spectral index of $\alpha_{144\,\text{MHz}}^{1.5\,\text{GHz}}=-1.4\pm0.5$ for the Pillow. If future observations confirm a slope as flat as the central value of -1.4 or even flatter, this would pose a severe challenge for the electron acceleration scenarios., Comment: 14 pages, 12 figures, accepted for publication in A&A
Published: 2021
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24. Dissecting nonthermal emission in the complex multiple-merger galaxy cluster Abell 2744: Radio and X-ray analysis

Author: A. Drabent, Denis Wittor, Felipe Andrade-Santos, Paola Domínguez-Fernández, R. J. van Weeren, M. Brienza, H. J. A. Röttgering, G. Brunetti, Marcus Brüggen, W. R. Formann, E. Bonnassieux, Matthias Hoeft, Annalisa Bonafede, A. S. Rajpurohit, Franco Vazza, C. J. Riseley, K. Rajpurohit, Rajpurohit K., Vazza F., Van Weeren R.J., Hoeft M., Brienza M., Bonnassieux E., Riseley C.J., Brunetti G., Bonafede A., Bruggen M., Formann W.R., Rajpurohit A.S., Rottgering H.J.A., Drabent A., Dominguez-Fernandez P., Wittor D., and Andrade-Santos F.
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Radiation mechanisms: non-thermal, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Radio spectrum, Galaxies: star clusters: individual: Abell 2744, Radio continuum: general, Radio relics, 0103 physical sciences, Surface brightness, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Physics, Spectral index, Giant Metrewave Radio Telescope, 010308 nuclear & particles physics, Astronomy and Astrophysics, Acceleration of particle, Radiation mechanisms: thermal, Abell 2744, Space and Planetary Science, Galaxies: clusters: general, Halo, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present the first deep low frequency radio observations of the massive and highly disturbed galaxy cluster Abell 2744 using the upgraded Giant Metrewave Radio Telescope (uGMRT). The cluster is experiencing a very complex multiple merger and hosts a giant halo and four radio relics. The uGMRT observations, together with existing VLA and Chandra observations, allow us to study the complexity of the physical mechanisms active in this system. Our new images reveal that the central halo emission is more extended toward low frequencies. We find that the integrated spectrum of the halo follows a power-law between 150 MHz and 3 GHz, while its subregions show significantly different spectra, also featuring high frequency spectral steepening. The halo also shows local regions in which the spectral index is significantly different from the average value. Our results highlight that an overall power-law spectrum, as observed in many radio halos, may also arise from the superposition of different subcomponents. The comparison of the radio surface brightness and spectral index with the X-ray brightness and temperature reveals for the first time different trends, indicating that the halo consists of two main components. All four relics in this system follow a power-law radio spectrum, compatible with shocks with Mach numbers in the range $3.0-4.5$. All relics are also highly polarized from 1-4 GHz and show low Faraday dispersion measures, suggesting that they are located in the outermost regions of the cluster. The complexity in the distribution and properties of nonthermal components in Abell 2744 supports a multiple merger scenario, as also highlighted by previous X-ray and lensing studies. Our unique results demonstrate the importance of sensitive and high-resolution, multi-frequency radio observations for understanding the interplay between the thermal and non-thermal components of the ICM., Comment: 24 pages, 19 figures, accepted for publication in A&A
Published: 2021
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25. Signatures from a merging galaxy cluster and its AGN population: LOFAR observations of Abell 1682

Author: T. M. Cantwell, Annalisa Bonafede, A. O. Clarke, Huub Röttgering, F. de Gasperin, Jeremy J. Harwood, A. Botteon, Timothy W. Shimwell, Marcus Brüggen, Gianfranco Brunetti, Cathy Horellou, Rossella Cassano, Matthias Hoeft, R. J. van Weeren, George Heald, Anna M. M. Scaife, Clarke A.O., Scaife A.M.M., Shimwell T., Van Weeren R.J., Bonafede A., Heald G., Brunetti G., Cantwell T.M., De Gasperin F., Bruggen M., Botteon A., Hoeft M., Horellou C., Cassano R., Harwood J.J., Rottgering H.J.A., and Astronomy
Subjects: Active galactic nucleus, Radiation mechanisms: non-thermal, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Population, galaxies: halos, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Galaxies: jet, 01 natural sciences, Radio continuum: galaxies, 0103 physical sciences, Cluster (physics), education, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, Spectral index, education.field_of_study, Quasars: supermassive black hole, 010308 nuclear & particles physics, quasars: supermassive black holes, Astronomy and Astrophysics, LOFAR, galaxies: jets, Astrophysics - Astrophysics of Galaxies, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Galaxies: halo, Galaxies: clusters: intracluster medium
Abstract: We present LOFAR data from 110--180~MHz of the merging galaxy cluster Abell 1682, alongside archival optical, radio and X-ray data. Our 6 arc-second resolution images at low frequencies reveal new structures associated with numerous radio galaxies in the cluster. At 20 arc-second resolution we see diffuse emission throughout the cluster over hundreds of kpc, indicating particle acceleration mechanisms are in play as a result of the cluster merger event and powerful active galactic nuclei. We show that a significant part of the cluster emission is from an old radio galaxy with very steep spectrum emission (having a spectral index of $\alpha < -2.5$). Furthermore we identify a new region of diffuse steep spectrum emission ($\alpha < -1.1$) as a candidate for a radio halo which is co-spatial with the centre of the cluster merger. We suggest its origin as a population of old and mildly relativistic electrons left over from radio galaxies throughout the cluster which have been re-accelerated to higher energies by shocks and turbulence induced by the cluster merger event. We also note the discovery of six new giant radio galaxies in the vicinity of Abell 1682., Comment: Accepted in A&A; see journal version for uncompressed figures
Published: 2019

26. The LOFAR Two-metre Sky Survey. IV. First Data Release: Photometric redshifts and rest-frame magnitudes

Author: Matthias Hoeft, Martin J. Hardcastle, Kenneth Duncan, Joseph R. Callingham, Philip Best, Glenn J. White, C. Tasse, G. Gürkan, Isabella Prandoni, Daniel J. Smith, Wendy L. Williams, D. Nisbet, R. J. van Weeren, Huub Röttgering, Matt J. Jarvis, Leah K. Morabito, George K. Miley, Dominik J. Schwarz, Timothy W. Shimwell, R. Kondapally, Beatriz Mingo, Rachel Cochrane, Krzysztof T. Chyzy, A. P. Mechev, Judith H. Croston, J. Sabater, L. Alegre, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), astro-ph.GA, media_common.quotation_subject, galaxies: active, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Source Population, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, media_common, astro-ph.HE, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), radio continuum: galaxies, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Rest frame, Astrophysics - Astrophysics of Galaxies, Redshift, galaxies [radio continuum], 13. Climate action, Space and Planetary Science, Sky, Astrophysics of Galaxies (astro-ph.GA), active [galaxies], astro-ph.CO, distances and redshifts [galaxies], galaxies: distances and redshifts, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Data release, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is a sensitive, high-resolution 120-168 MHz survey of the Northern sky. The LoTSS First Data Release (DR1) presents 424 square degrees of radio continuum observations over the HETDEX Spring Field (10h45m00s $ 0.15$) of 7.9%. We also find that, at a given redshift, there is no strong trend in photo-$z$ quality as a function of radio luminosity. However there are strong trends as a function of redshift for a given radio luminosity, a result of selection effects in the spectroscopic sample and/or intrinsic evolution within the radio source population. Additionally, for the sample of sources in the LoTSS First Data Release with optical counterparts, we present rest-frame optical and mid-infrared magnitudes based on template fits to the consensus photometric (or spectroscopic when available) redshift., Comment: 16 figures, 1 table and 18 pages. This paper is part of the LOFAR surveys Data Release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, Volume 622. The catalogues and images from the data release will be publicly available at http://www.lofar-surveys.org upon publication of the volume
Published: 2019
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27. The LOFAR Two-metre Sky Survey. II. First data release

Author: Eskil Varenius, Huub Röttgering, Magdalena Kunert-Bajraszewska, Ricardo Genova-Santos, Judith H. Croston, D. Nisbet, R. Lakhoo, R. Kondapally, F. Savini, Joseph R. Callingham, A. O. Clarke, H. R. Stacey, M. H. D. van der Wiel, Isabella Prandoni, Antonia Rowlinson, R. Pizzo, Gianfranco Brunetti, David Bacon, George K. Miley, Marcus Brüggen, L. Alegre, R.-J. Dettmar, C. Dumba, R. J. van Weeren, Volker Heesen, Stephen Bourke, G. Calistro Rivera, A. Botteon, J. Sabater, M. Mirmont, G. Gürkan, Andrea Merloni, Torsten A. Enßlin, Marek Jamrozy, Philip Best, A. Drabent, Marcellin Atemkeng, Glenn J. White, R. C. Vermeulen, Wolfgang Reich, Neal Jackson, Chiara Ferrari, Marco Iacobelli, Huib Intema, J. B. R. Oonk, D. N. Hoang, John Conway, A. Wilber, Marisa Brienza, T. J. Dijkema, B. Webster, M. A. Garrett, Simon Perkins, A. P. Mechev, Shane O'Sullivan, Christopher J. Conselice, I. van Bemmel, Annalisa Bonafede, Oleg Smirnov, John L. Quinn, John McKean, G. Kokotanekov, Subhash C. Mandal, Daniel J. Smith, C. L. Hale, Arti Goyal, Błażej Nikiel-Wroczyński, K. L. Emig, S. Urquhart, Marijke Haverkorn, Timothy W. Shimwell, R. Morganti, Michael W. Wise, Elizabeth K. Mahony, Beatriz Mingo, Arpad Miskolczi, C. A. Jackson, Leah K. Morabito, D. A. Rafferty, A. Saxena, C. Roskowinski, Rachel Cochrane, C. Schrijvers, M. Mevius, Wendy L. Williams, E. Bonnassieux, Rossella Cassano, Matthias Hoeft, Krzysztof T. Chyzy, Dominik J. Schwarz, B. Hugo, Robert Beswick, George Heald, C. Tasse, S. Mooney, Jeremy J. Harwood, Emanuela Orru, Martin J. Hardcastle, Kenneth Duncan, S. S. Sridhar, Cathy Horellou, Matt J. Jarvis, L. Bester, F. de Gasperin, Aleksandar Shulevski, A. Danezi, V. H. Mahatma, Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Astronomy, Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Shimwell T.W., Tasse C., Hardcastle M.J., Mechev A.P., Williams W.L., Best P.N., Rottgering H.J.A., Callingham J.R., Dijkema T.J., De Gasperin F., Hoang D.N., Hugo B., Mirmont M., Oonk J.B.R., Prandoni I., Rafferty D., Sabater J., Smirnov O., Van Weeren R.J., White G.J., Atemkeng M., Bester L., Bonnassieux E., Bruggen M., Brunetti G., Chy K.T., Cochrane R., Conway J.E., Croston J.H., Danezi A., Duncan K., Haverkorn M., Heald G.H., Iacobelli M., Intema H.T., Jackson N., Jamrozy M., Jarvis M.J., Lakhoo R., Mevius M., Miley G.K., Morabito L., Morganti R., Nisbet D., Orru E., Perkins S., Pizzo R.F., Schrijvers C., Smith D.J.B., Vermeulen R., Wise M.W., Alegre L., Bacon D.J., Van Bemmel I.M., Beswick R.J., Bonafede A., Botteon A., Bourke S., Brienza M., Calistro Rivera G., Cassano R., Clarke A.O., Conselice C.J., Dettmar R.J., Drabent A., Dumba C., Emig K.L., Ensslin T.A., Ferrari C., Garrett M.A., Genova-Santos R.T., Goyal A., Gurkan G., Hale C., Harwood J.J., Heesen V., Hoeft M., Horellou C., Jackson C., Kokotanekov G., Kondapally R., Kunert-Bajraszewska M., Mahatma V., Mahony E.K., Mandal S., McKean J.P., Merloni A., Mingo B., Miskolczi A., Mooney S., Nikiel-Wroczynski B., O'Sullivan S.P., Quinn J., Reich W., Roskowinski C., Rowlinson A., Savini F., Saxena A., Schwarz D.J., Shulevski A., Sridhar S.S., Stacey H.R., Urquhart S., Van Der Wiel M.H.D., Varenius E., Webster B., and Wilber A.
Subjects: Astronomy, radio continuum: general, Flux, techniques: image processing, Astrophysics, 01 natural sciences, CLUSTER ENVIRONMENTS, ST/M001229/1, Survey, 010303 astronomy & astrophysics, SOUTHERN SKY, media_common, astro-ph.HE, Physics, CALIBRATION, High Energy Astrophysical Phenomena (astro-ph.HE), image processing [techniques], UNDERSTANDING RADIO POLARIMETRY, ST/R00109X/1, ST/P000096/1, astro-ph.CO, general [radio continuum], Catalog, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics, Noise (radio), Astrophysics - Cosmology and Nongalactic Astrophysics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), astro-ph.GA, media_common.quotation_subject, FOS: Physical sciences, Declination, surveys, 0103 physical sciences, [PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det], AGN, Instrumentation and Methods for Astrophysics (astro-ph.IM), STFC, ST/M001326/1, 010308 nuclear & particles physics, RCUK, Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, Galaxy, Redshift, GALAXY, ST/M001008/1, Space and Planetary Science, Sky, IMAGING SURVEY, DISCOVERY, Astrophysics of Galaxies (astro-ph.GA), FLUX-DENSITY SCALE, Right ascension, EMISSION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], catalogs, astro-ph.IM
Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is an ongoing sensitive, high-resolution 120-168MHz survey of the entire northern sky for which observations are now 20% complete. We present our first full-quality public data release. For this data release 424 square degrees, or 2% of the eventual coverage, in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45$^\circ$00$'$00$''$ to 57$^\circ$00$'$00$''$) were mapped using a fully automated direction-dependent calibration and imaging pipeline that we developed. A total of 325,694 sources are detected with a signal of at least five times the noise, and the source density is a factor of $\sim 10$ higher than the most sensitive existing very wide-area radio-continuum surveys. The median sensitivity is S$_{\rm 144 MHz} = 71\,\mu$Jy beam$^{-1}$ and the point-source completeness is 90% at an integrated flux density of 0.45mJy. The resolution of the images is 6$''$ and the positional accuracy is within 0.2$''$. This data release consists of a catalogue containing location, flux, and shape estimates together with 58 mosaic images that cover the catalogued area. In this paper we provide an overview of the data release with a focus on the processing of the LOFAR data and the characteristics of the resulting images. In two accompanying papers we provide the radio source associations and deblending and, where possible, the optical identifications of the radio sources together with the photometric redshifts and properties of the host galaxies. These data release papers are published together with a further $\sim$20 articles that highlight the scientific potential of LoTSS., Comment: 16 figures, 1 table and 22 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal
Published: 2019
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28. First detection of frequency-dependent, time-variable dispersion measures

Author: Stefan Oslowski, J. Künsemöller, Arpad Miskolczi, Joris P. W. Verbiest, Jean-Mathias Grießmeier, Matthias Hoeft, Caterina Tiburzi, J. M. Anderson, A. Horneffer, Michael Kramer, D. Michilli, Jason W. T. Hessels, M. Serylak, J. Y. Donner, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Frequency band, Astrophysics::High Energy Astrophysical Phenomena, ISM: structure, FOS: Physical sciences, Context (language use), Electron, Astrophysics, 01 natural sciences, ISM: clouds, 0103 physical sciences, Dispersion (optics), 010303 astronomy & astrophysics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Line-of-sight, 010308 nuclear & particles physics, Scattering, pulsars: individual: PSR J2219+4754, Astronomy and Astrophysics, LOFAR, Refraction, Astrophysics - Astrophysics of Galaxies, 13. Climate action, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena
Abstract: Context. High-precision pulsar-timing experiments are affected by temporal variations of the Dispersion Measure (DM), which are related to spatial variations in the interstellar electron content. Correcting for DM variations relies on the cold-plasma dispersion law which states that the dispersive delay varies with the squared inverse of the observing frequency. This may however give incorrect measurements if the probed electron content (and therefore the DM) varies with observing frequency, as is predicted theoretically. Aims. We study small-scale density variations in the ionised interstellar medium. These structures may lead to frequency-dependent DMs in pulsar signals and could inhibit the use of lower-frequency pulsar observations to correct time-variable interstellar dispersion in higher-frequency pulsar-timing data. Methods. We used high-cadence, low-frequency observations with three stations from the German LOng-Wavelength (GLOW) consortium, which are part of the LOw Frequency ARray (LOFAR). Specifically, 3.5 years of weekly observations of PSR J2219+4754 are presented. Results. We present the first detection of frequency-dependent DMs towards any interstellar object and a precise multi-year time-series of the time- and frequency-dependence of the measured DMs. The observed DM variability is significant and may be caused by extreme scattering events. Potential causes for frequency-dependent DMs are quantified and evaluated. Conclusions. We conclude that frequency-dependence of DMs has been reliably detected and is caused by small-scale (up to 10s of AUs) but steep density variations in the interstellar electron content. We find that long-term trends in DM variability equally affect DMs measured at both ends of our frequency band and hence the negative impact on long-term high-precision timing projects is expected to be limited., to be published in A&A (accepted 2019-02-06), 11 pages, 7 figures, update: A&A language editing, typos
Published: 2019
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29. Polarization of radio relics in galaxy clusters

Author: Marcus Brüggen, Franco Vazza, P. Dominguez-Fernandez, D. Wittor, Matthias Hoeft, Wittor, D, Hoeft, M, Vazza, F, Brüggen, M, and Domínguez-Fernández, P
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), MHD, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, High resolution, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Electron, 01 natural sciences, symbols.namesake, Radio relics, 0103 physical sciences, Faraday effect, Astrophysics - Cosmology and Nongalactic Astrophysic, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Physics, polarization, 010308 nuclear & particles physics, Astronomy and Astrophysics, Polarization (waves), Astrophysics - Astrophysics of Galaxies, galaxies: clusters: individual: radio relic, Magnetic field, Space and Planetary Science, galaxies: cluster, Astrophysics of Galaxies (astro-ph.GA), symbols, Magnetohydrodynamics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio emission in the form of giant radio relics is observed at the periphery of galaxy clusters. This non-thermal emission is an important tracer for cosmic-ray electrons and intracluster magnetic fields. One striking observational feature of these objects is their high degree of polarisation which provides information on the magnetic fields at the relics' positions. In this contribution, we test if state-of-the-art high resolution cosmological simulations are able to reproduce the polarisation features of radio relics. Therefore, we present a new analysis of high-resolution cosmological simulations to study the polarisation properties of radio relics in detail. In order to compare our results with current and future radio observations, we create mock radio observations of the diffuse polarised emission from a massive galaxy clusters using six different projections, for different observing frequencies and for different telescopes. Our simulations suggest that, due to the effect of Faraday rotation, it is extremely difficult to relate the morphology of the polarised emission for observing frequencies below $1.4 \ \mathrm{GHz}$ to the real magnetic field structure in relics. We can reproduce the observed degree of polarisation and also several small-scale structures observed in real radio relics, but further work would be needed to reproduce some large-scale spectacular features as observed in real radio relics, such as the "Sausage" and the "Toothbrush" relics., Comment: Accepted for publication in MNRAS, 20 pages, 13 figures
Published: 2019
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30. Radio observations of the merging galaxy cluster Abell 520

Author: Andra Stroe, H. J. A. Röttgering, A. Drabent, Gianfranco Brunetti, Rossella Cassano, Matthias Hoeft, Marcus Brüggen, D. A. Rafferty, Timothy W. Shimwell, Huib Intema, F. de Gasperin, A. Shweta, A. Botteon, D. N. Hoang, Felipe Andrade-Santos, and R. J. van Weeren
Subjects: Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Giant Metrewave Radio Telescope, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy and Astrophysics, LOFAR, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Relativistic particle, Particle acceleration, Radio halo, Space and Planetary Science, 0103 physical sciences, Abell 520, Surface brightness, Astrophysics - High Energy Astrophysical Phenomena, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics
Abstract: We examine the possible acceleration mechanisms of the relativistic particles responsible for the extended radio emission in Abell 520. We used new LOFAR 145 MHz, archival GMRT 323 MHz and VLA 1.5 GHz data to study the morphological and spectral properties of extended cluster emission. The observational properties are discussed in the framework of particle acceleration models associated with cluster merger turbulence and shocks. In Abell 520, we confirm the presence of extended synchrotron radio emission that has been classified as a radio halo. The comparison between the radio and X-ray brightness suggests that the halo might originate in a cocoon rather than from the central X-ray bright regions of the cluster. The halo spectrum is roughly uniform on the scale of 66 kpc. There is a hint of spectral steepening from the SW edge towards the cluster centre. Assuming DSA, the radio data are suggestive of a shock of $\mathcal{M}_{SW}=2.6_{-0.2}^{+0.3}$ that is consistent with the X-ray derived estimates. This is in line with the scenario in which relativistic electrons in the SW radio edge gain their energies at the shock front via acceleration of either thermal or fossil electrons. We do not detect extended radio emission ahead of the SW shock that is predicted if the emission is the result of adiabatic compression. An X-ray surface brightness discontinuity is detected towards the NE region that may be a counter shock of $\mathcal{M}_{NE}^{X}=1.52\pm0.05$. This is lower than the value predicted from the radio emission ($\mathcal{M}_{NE}=2.1\pm0.2$). Our observations indicate that the SW radio emission in Abell 520 is likely effected by the prominent X-ray detected shock in which radio emitting particles are (re-)accelerated through the Fermi-I mechanism. The NE X-ray discontinuity that is approximately collocated with an edge in the radio emission hints at the presence of a counter shock., Comment: 8 figures, 2 tables and 11 pages. This paper is part of the LOFAR surveys data release 1 and has been accepted for publication in a special edition of A&A that will appear in Feb 2019, volume 622. The catalogues and images from the data release will be publicly available on lofar-surveys.org upon publication of the journal
Published: 2019

31. Particle re-acceleration and Faraday-complex structures in the RXC J1314.4-2515 galaxy cluster

Author: Nathan Golovich, A. Botteon, R. J. van Weeren, Franco Vazza, D. Wittor, Nicola Locatelli, F. de Gasperin, Daniele Dallacasa, C. Stuardi, Marcus Brüggen, Annalisa Bonafede, Matthias Hoeft, Stuardi, C, Bonafede, A, Wittor, D, Vazza, F, Botteon, A, Locatelli, N, Dallacasa, D, Golovich, N, Hoeft, M, van Weeren, R J, Brüggen, M, and de Gasperin, F
Subjects: Shock wave, Cosmology and Nongalactic Astrophysics (astro-ph.CO), shock wave, Radio galaxy, galaxies: clusters: individual: RXC J1314.4-2515, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, magnetic field, Astrophysics, Electron, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio relics, 0103 physical sciences, 010303 astronomy & astrophysics, Galaxy cluster, acceleration of particle, Astrophysics::Galaxy Astrophysics, Physics, polarization, Line-of-sight, 010308 nuclear & particles physics, Astronomy and Astrophysics, radiation mechanisms: non-thermal, Polarization (waves), Astrophysics - Astrophysics of Galaxies, Magnetic field, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics are sites of electron (re)acceleration in merging galaxy clusters but the mechanism of acceleration and the topology of the magnetic field in and near relics are yet to be understood. We are carrying out an observational campaign on double relic galaxy clusters starting with RXC J1314.4-2515. With $Jansky Very Large Array$ multi-configuration observations in the frequency range 1-4 GHz, we perform both spectral and polarization analyses, using the Rotation Measure synthesis technique. We use archival $XMM-Newton$ observations to constrain the properties of the shocked region. We discover a possible connection between the activity of a radio galaxy and the emission of the eastern radio relic. In the northern elongated arc of the western radio relic, we detect polarized emission with an average polarization fraction of $31 \ \%$ at 3 GHz and we derive the Mach number of the underlying X-ray shock. Our observations reveal low levels of fractional polarization and Faraday-complex structures in the southern region of the relic, which point to the presence of thermal gas and filamentary magnetic field morphology inside the radio emitting volume. We measured largely different Rotation Measure dispersion from the two relics. Finally, we use cosmological magneto-hydrodynamical simulations to constrain the magnetic field, viewing angle, and to derive the acceleration efficiency of the shock. We find that the polarization properties of RXC J1314.4-2515 are consistent with a radio relic observed at $70^{\circ}$ with respect to the line of sight and that efficient re-acceleration of fossil electrons has taken place., 24 pages, 19 figures, 5 tables, accepted for publication in MNRAS
Published: 2019
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32. A radio ridge connecting two galaxy clusters in a filament of the cosmic web

Author: L. Feretti, Timothy W. Shimwell, R. Pizzo, H. J. A. Röttgering, Michael W. Wise, Gianni Bernardi, Matteo Murgia, Serena Manti, Claudio Gheller, Anna M. M. Scaife, H. Junklewitz, Gianfranco Brunetti, Franco Vazza, Marco Iacobelli, V. Vacca, Rossella Cassano, Matthias Hoeft, Rosita Paladino, Federica Govoni, Annalisa Bonafede, Marcus Brüggen, Emanuela Orru, Gabriele Giovannini, Chiara Ferrari, F. Loi, F. de Gasperin, Cathy Horellou, R. J. van Weeren, Torsten A. Enßlin, Govoni F., Orru E., Bonafede A., Iacobelli M., Paladino R., Vazza F., Murgia M., Vacca V., Giovannini G., Feretti L., Loi F., Bernardi G., Ferrari C., Pizzo R.F., Gheller C., Manti S., Bruggen M., Brunetti G., Cassano R., De Gasperin F., Ensslin T.A., Hoeft M., Horellou C., Junklewitz H., Rottgering H.J.A., Scaife A.M.M., Shimwell T.W., Van Weeren R.J., and Wise M.
Subjects: nearby, shock acceleration, binary cluster, Astrophysics::High Energy Astrophysical Phenomena, Population, relics, FOS: Physical sciences, Electron, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Relativistic particle, Protein filament, 0103 physical sciences, emission, 010306 general physics, education, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, education.field_of_study, geography, magnetic fields, radio observations, Multidisciplinary, geography.geographical_feature_category, cd clusters, LOFAR, dynamics, Astrophysics - Astrophysics of Galaxies, Magnetic field, Ridge, Astrophysics of Galaxies (astro-ph.GA)
Abstract: Galaxy clusters are the most massive gravitationally bound structures in the Universe. They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intra-cluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low Frequency Array (LOFAR) at 140 MHz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may re-accelerate a pre-existing population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge., Comment: Published in Science
Published: 2019

33. LOFAR, VLA, and Chandra Observations of the Toothbrush Galaxy Cluster

Author: H. J. A. Röttgering, Christine Jones, Laura Birzan, William A. Dawson, Georgiana A. Ogrean, J. Sabater, Judith H. Croston, Torsten A. Ensslin, S. S. Murray, T. J. Dijkema, Martin J. Hardcastle, S. S. Sridhar, S. van der Tol, Lawrence Rudnick, Roberto Pizzo, Marcus Brüggen, Rossella Cassano, Cathy Horellou, Maaijke Mevius, Aurora Simionescu, William R. Forman, Craig L. Sarazin, George Heald, Glenn J. White, Krzysztof T. Chyzy, Emanuela Orrú, Andra Stroe, G. K. Miley, Annalisa Bonafede, Wendy L. Williams, D. A. Rafferty, Hubertus Intema, G. Brunetti, Timothy W. Shimwell, Felipe Andrade-Santos, R. J. van Weeren, Philip Best, Chiara Ferrari, Matthias Hoeft, Ralph P. Kraft, Matt J. Jarvis, F. de Gasperin, Astronomy, Van Weeren, R.J., Brunetti, G., Brüggen, M., Andrade-Santos, F., Ogrean, G.A., Williams, W.L., Röttgering, H.J.A., Dawson, W.A., Forman, W.R., Gasperin, F. De, Hardcastle, M.J., Jones, C., Miley, G.K., Rafferty, D.A., Rudnick, L., Sabater, J., Sarazin, C.L., Shimwell, T.W., Bonafede, A., Best, P.N., Birzan, L., Cassano, R., Chyzy, K.T., Croston, J.H., Dijkema, T.J., Enßlin, T., Ferrari, C., Heald, G., Hoeft, M., Horellou, C., Jarvis, M.J., Kraft, R.P., Mevius, M., Intema, H.T., Murray, S.S., Orrú, E., Pizzo, R., Sridhar, S.S., Simionescu, A., Stroe, A., Tol, S. Van Der, and White, G.J.
Subjects: clusters: individual: RX J0603.3+4214 [galaxies], Cosmology and Nongalactic Astrophysics (astro-ph.CO), galaxies: clusters: intracluster medium, Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, galaxies: clusters: individual: RX J0603.3+4214, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Radio relics, 0103 physical sciences, education, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, large-scale structure of universe, education.field_of_study, Spectral index, 010308 nuclear & particles physics, galaxies: clusters: individual (RX J0603.3+4214), largescale structure of universe, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, radiation mechanisms: non-thermal, non-thermal [radiation mechanisms], X-rays: galaxies: cluster, Particle acceleration, Radio halo, clusters: intracluster medium [galaxies], Space and Planetary Science, X-rays: galaxies: clusters, large-scale structure of Universe, galaxies: clusters [X-rays], Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: 著者人数: 42名, Accepted: 2016-01-18, 資料番号: SA1160090000
Published: 2016

34. Search for low-frequency diffuse radio emission around a shock in the massive galaxy cluster MACS J0744.9+3927

Author: Annalisa Bonafede, L. Bîrzan, R. J. van Weeren, Marcus Brüggen, A. Botteon, F. de Gasperin, D. Rafferty, F. Savini, G. Brunetti, Rossella Cassano, Timothy W. Shimwell, Denis Wittor, Matthias Hoeft, A. Wilber, Wilber, A., Brüggen, M., Bonafede, A., Rafferty, D., Savini, F., Shimwell, T., van Weeren, R.J., Botteon, A., Cassano, R., Brunetti, G., De Gasperin, F., Wittor, D., Hoeft, M., and Birzan, L.
Subjects: Solar System, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Electron, Astrophysics::Cosmology and Extragalactic Astrophysics, Low frequency, Astro-physics/chemistry/biology, solar system, stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation [PE9 - Universe Sciences], Radio continuum: galaxie, 01 natural sciences, symbols.namesake, Intracluster medium, 0103 physical sciences, Galaxies: clusters: individual: MACS J0744.9+3927, 010303 astronomy & astrophysics, Galaxy cluster, Computer Science::Databases, Astrophysics::Galaxy Astrophysics, Physics, Shock (fluid dynamics), 010308 nuclear & particles physics, Astronomy and Astrophysics, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Mach number, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), symbols, Galaxies: clusters: general, Radio frequency, Galaxies: clusters: intracluster medium, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Merging galaxy clusters produce low Mach number shocks in the intracluster medium. These shocks can accelerate electrons to relativistic energies that are detectable at radio frequencies. MACS J0744.9+3927 is a massive ($M_{500} = (11.8 \pm 2.8) \times 10^{14} M_{\odot}$), high-redshift ($z=0.6976$) cluster where a Bullet-type merger is presumed to have taken place. Sunyaev-Zel'dovich maps from MUSTANG indicate that a shock, with Mach number $\mathcal{M} = 1.0-2.9$ and an extension of $\sim 200$ kpc, sits near the centre of the cluster. The shock is also detected as a brightness and temperature discontinuity in X-ray observations. To search for diffuse radio emission associated with the merger, we have imaged the cluster with the LOw Frequency ARray (LOFAR) at 120-165 MHz. Our LOFAR radio images reveal previously undetected AGN emission, but do not show clear cluster-scale diffuse emission in the form of a radio relic nor a radio halo. The region of the shock is on the western edge of AGN lobe emission from the brightest cluster galaxy. Correlating the flux of known shock-induced radio relics versus their size, we find that the radio emission overlapping the shocked region in MACS J0744.9+3927 is likely of AGN origin. We argue against the presence of a relic caused by diffusive shock acceleration and suggest that the shock is too weak to accelerate electrons from the intracluster medium., 11 pages, 9 figures, accepted to MNRAS on February 13, 2018
Published: 2018

35. Discovery of large-scale diffuse radio emission in low-mass galaxy cluster Abell 1931

Author: G. Brunetti, Annalisa Bonafede, H. J. A. Röttgering, F. Savini, F. de Gasperin, Shane O'Sullivan, Timothy W. Shimwell, D. Rafferty, Huib Intema, Torsten A. Ensslin, R. J. van Weeren, Marcus Brüggen, G. Di Gennaro, Matthias Hoeft, A. Wilber, Brüggen, M., Bonafede, A., van Weeren, R.J., Shimwell, T., Intema, H., Röttgering, H., Brunetti, G., Di Gennaro, G., Savini, F., Wilber, A., O'Sullivan, S., Ensslin, T.A., De Gasperin, F., and Hoeft, M.
Subjects: Radio galaxy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, 01 natural sciences, Luminosity, 0103 physical sciences, Brightest cluster galaxy, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Intergalactic medium, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Spectral index, 010308 nuclear & particles physics, Astronomy and Astrophysics, Radiation mechanisms: Nonthermal, LOFAR, Astronomy and Astrophysic, Acceleration of particle, Astrophysics - Astrophysics of Galaxies, Radio continuum: Galaxies -X-rays: Galaxies: Cluster, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Elliptical galaxy, Low Mass, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Extended, steep-spectrum radio synchrotron sources are pre-dominantly found in massive galaxy clusters as opposed to groups. LOFAR Two-Metre Sky Survey images have revealed a diffuse, ultra-steep spectrum radio source in the low-mass cluster Abell 1931. The source has a fairly irregular morphology with a largest linear size of about 550 kpc. The source is only seen in LOFAR observations at 143 MHz and GMRT observations at 325 MHz. The spectral index of the total source between 143 MHz and 325 MHz is $\alpha_{143}^{325} = -2.86 \pm 0.36$. The source remains invisible in Very Large Array (1-2 GHz) observations as expected given the spectral index. Chandra X-ray observations of the cluster revealed a bolometric luminosity of $L_X = (1.65 \pm 0.39) \times 10^{43}$ erg s$^{-1}$ and a temperature of $2.92_{-0.87}^{+1.89}$ keV which implies a mass of around $\sim 10^{14} M_{\odot}$. We conclude that the source is a remnant radio galaxy that has shut off around 200 Myr ago. The brightest cluster galaxy, a radio-loud elliptical galaxy, could be the source for this extinct source. Unlike remnant sources studied in the literature, our source has a steep spectrum at low radio frequencies. Studying such remnant radio galaxies at low radio frequencies is important for understanding the scarcity of such sources and their role in feedback processes., Comment: MNRAS, in press
Published: 2018
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36. Shock location and CME 3D reconstruction of a solar type II radio burst with LOFAR

Author: M. C. Toribio, B. Ciardi, J. M. Anderson, Eduard P. Kontar, Karl-Ludwig Klein, Charlotte Sobey, Jochen Eislöffel, Marian Soida, Marco Iacobelli, P. Zarka, A. P. Rouillard, R. Blaauw, A. G. Polatidis, R. J. van Weeren, Mario M. Bisi, A. W. Gunst, E. de Geus, Mark J. Bentum, Oleg Smirnov, Henk Mulder, R. Pizzo, Aris Karastergiou, F. Breitling, Pietro Zucca, Jörg R. Hörandel, Hanna Rothkaehl, Peter T. Gallagher, H. Munk, Bartosz Dabrowski, Martin Bell, Olaf Wucknitz, Anna Nelles, R. Vermeulen, Jean-Mathias Grießmeier, Marcus Brüggen, Ashish Asgekar, V. N. Pandey, H. Paas, Jasmina Magdalenic, Richard Fallows, Matthias Hoeft, Christian Vocks, Philip Best, J. W. Broderick, Harvey Butcher, J. Sluman, D. McKay-Bukowski, E. Juette, M. A. Garrett, Andrzej Krankowski, Satyendra Thoudam, Antonia Rowlinson, R. Pekal, S. Duscha, Eoin P. Carley, Adam T. Deller, Dominik J. Schwarz, Wolfgang Reich, J. van Leeuwen, Emanuela Orru, Diana E. Morosan, Aleksandar Shulevski, Gottfried Mann, George Heald, W. N. Brouw, Netherlands Institute for Radio Astronomy (ASTRON), Trinity College Dublin, Institut de recherche en astrophysique et planétologie (IRAP), Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Observatoire Midi-Pyrénées (OMP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA (UMR_8109)), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Leibniz-Institut für Astrophysik Potsdam (AIP), STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Space Research Centre of Polish Academy of Sciences (CBK), Polska Akademia Nauk (PAN), Space Radio-Diagnostic Research Center [Olsztyn], University of Warmia and Mazury [Olsztyn], School of Physics and Astronomy [Southampton], University of Southampton, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Universität Hamburg (UHH), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Radboud university [Nijmegen], Ruhr-Universität Bochum [Bochum], Oxford Astrophysics, University of Oxford [Oxford], University of Tromsø (UiT), Max-Planck-Institut für Radioastronomie (MPIFR), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Center for Wireless Technology Eindhoven, Electromagnetics, EM for Radio Science Lab, High Energy Astrophys. & Astropart. Phys (API, FNWI), Astronomy, Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France -Centre National de la Recherche Scientifique (CNRS), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Polska Akademia Nauk = Polish Academy of Sciences (PAN), Universiteit Leiden, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Radboud University [Nijmegen], University of Oxford, ANR-17-CE31-0006,COROSHOCK,EVALUER LE ROLE DU CHOC COMME ACCELERATEUR DE PARTICULES SOLAIRES(2017), Institut national des sciences de l'Univers (INSU - CNRS)-Université Toulouse III - Paul Sabatier (UT3), Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Météo France-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), and Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)
Subjects: 010504 meteorology & atmospheric sciences, corona [Sun], Sun: coronal mass ejections (CMEs), Astronomy, Astrophysics::High Energy Astrophysical Phenomena, WAVES, Interplanetary medium, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, Computer Science::Digital Libraries, 01 natural sciences, VDP::Matematikk og Naturvitenskap: 400::Fysikk: 430::Astrofysikk, astronomi: 438, 0103 physical sciences, Coronal mass ejection, Astrophysics::Solar and Stellar Astrophysics, 010303 astronomy & astrophysics, SUN-EARTH CONNECTION, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences, Physics, Science & Technology, Sun: radio radiation, ORIGIN, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], radio radiation [Sun], Sun: corona, Astrophysics::Instrumentation and Methods for Astrophysics, TRANSIENTS, Astronomy and Astrophysics, LOFAR, Corona, Physics::History of Physics, coronal mass ejections (CMEs) [Sun], VDP::Mathematics and natural science: 400::Physics: 430::Astrophysics, astronomy: 438, CORONAL MASS EJECTIONS, Radio propagation, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Physical Sciences, FLARES, Physics::Space Physics, X-RAY, Large Angle and Spectrometric Coronagraph, EMISSION, Heliosphere, Radio wave
Abstract: Type II radio bursts are evidence of shocks in the solar atmosphere and inner heliosphere that emit radio waves ranging from sub-meter to kilometer lengths. These shocks may be associated with CMEs and reach speeds higher than the local magnetosonic speed. Radio imaging of decameter wavelengths (20-90 MHz) is now possible with LOFAR, opening a new radio window in which to study coronal shocks that leave the inner solar corona and enter the interplanetary medium and to understand their association with CMEs. To this end, we study a coronal shock associated with a CME and type II radio burst to determine the locations at which the radio emission is generated, and we investigate the origin of the band-splitting phenomenon., Comment: 7 Figures, 9 Pages
Published: 2018
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37. Low-frequency pulse profile variation in PSR B2217+47: evidence for echoes from the interstellar medium

Author: J. Y. Donner, Benjamin Stappers, Daniel R. Stinebring, Patrick Weltevrede, B. Shaw, Daniele Michilli, Jason W. T. Hessels, J.-M. Grießmeier, Adam Deller, Maura Pilia, Joris P. W. Verbiest, Matthias Hoeft, Aris Karastergiou, Laura Driessen, M. Serylak, L. Bondonneau, M. Geyer, S. Sanidas, Stefan Oslowski, Michael Kramer, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), High Energy Astrophys. & Astropart. Phys (API, FNWI), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace ( LPC2E ), Centre National de la Recherche Scientifique ( CNRS ) -Université d'Orléans ( UO ) -Institut national des sciences de l'Univers ( INSU - CNRS ), Unité Scientifique de la Station de Nançay ( USN ), and Institut national des sciences de l'Univers ( INSU - CNRS ) -Observatoire de Paris-Université d'Orléans ( UO ) -Centre National de la Recherche Scientifique ( CNRS )
Subjects: Electron density, [ PHYS.ASTR ] Physics [physics]/Astrophysics [astro-ph], Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Astrophysics, Low frequency, 01 natural sciences, Pulsar, 0103 physical sciences, education, 010303 astronomy & astrophysics, ISM: general, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, education.field_of_study, pulsars: individual: PSR B2217+47, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, Interstellar medium, radio continuum: ISM, 13. Climate action, Space and Planetary Science, Circular symmetry, Astrophysics - High Energy Astrophysical Phenomena, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Order of magnitude
Abstract: We have observed a complex and continuous change in the integrated pulse profile of PSR B2217+47, manifested as additional components trailing the main peak. These transient components are detected over 6 years at $150$ MHz using the LOw Frequency ARray (LOFAR), but they are not seen in contemporaneous Lovell observations at $1.5$ GHz. We argue that propagation effects in the ionized interstellar medium (IISM) are the most likely cause. The putative structures in the IISM causing the profile variation are roughly half-way between the pulsar and the Earth and have transverse radii $R \sim 30$ AU. We consider different models for the structures. Under the assumption of spherical symmetry, their implied average electron density is $\overline{n}_e \sim 100$ cm$^{-3}$. Since PSR B2217+47 is more than an order of magnitude brighter than the average pulsar population visible to LOFAR, similar profile variations would not have been identified in most pulsars, suggesting that subtle profile variations in low-frequency profiles might be more common than we have observed to date. Systematic studies of these variations at low frequencies can provide a new tool to investigate the proprieties of the IISM and the limits to the precision of pulsar timing., to be published in MNRAS
Published: 2018
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38. Radio observations of the double-relic galaxy cluster Abell 1240

Author: D. N. Hoang, Felipe Andrade-Santos, Rossella Cassano, H. J. A. Röttgering, R. J. van Weeren, Timothy W. Shimwell, Huib Intema, G. Brunetti, Annalisa Bonafede, Marcus Brüggen, William A. Dawson, P. N. Best, A. Botteon, F. de Gasperin, Hiroki Akamatsu, Glenn J. White, Andra Stroe, Nathan Golovich, Matthias Hoeft, Hoang, D N, Shimwell, T W, van Weeren, R J, Intema, H T, Röttgering, H J A, Andrade-Santos, F, Akamatsu, H, Bonafede, A, Brunetti, G, Dawson, W A, Golovich, N, Best, P N, Botteon, A, Brüggen, M, Cassano, R, de Gasperin, F, Hoeft, M, Stroe, A, and White, G J
Subjects: Shock wave, Cosmology and Nongalactic Astrophysics (astro-ph.CO), shock wave, galaxies: clusters: intracluster medium, Astrophysics::High Energy Astrophysical Phenomena, Population, FOS: Physical sciences, Flux, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, galaxies: clusters: individual: Abell 1240, 01 natural sciences, Radio relics, 0103 physical sciences, education, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, education.field_of_study, 010308 nuclear & particles physics, Astronomy and Astrophysics, LOFAR, radiation mechanisms: non-thermal, Astrophysics - Astrophysics of Galaxies, diffuse radiation, Particle acceleration, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), large-scale structure of Universe, Halo, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We present LOw Frequency Array 120-168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the Giant Metrewave Radio Telescope 595-629MHz and Very Large Array 2-4GHz data, we characterized the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration, we obtain shock Mach numbers of M = 2.4 and 2.3 for the northern and southern shocks, respectively. For M less than or similar to 3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (> 10 per cent) particle acceleration efficiency required. However, for M greater than or similar to 4 shocks the required efficiency is greater than or similar to 1 per cent and greater than or similar to 0.5 per cent, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to >= 53 +/- 3 degrees and >= 39 +/- 5 degrees for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (similar to 1.8 Mpc) our upper limit on the power is P-1.4 (GHz) = (1.4 +/- 0.6) x 10(23) W Hz(-1) which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.
Published: 2018
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39. Exploring the making of a galactic wind in the star-bursting dwarf irregular galaxy IC 10 with LOFAR

Author: Luke Hindson, Rainer Beck, D. Rafferty, Fatemeh Tabatabaei, Jonathan Westcott, Rosita Paladino, Błażej Nikiel-Wroczyński, Elias Brinks, George Heald, Marcus Brüggen, A. Horneffer, Aritra Basu, Andrew Fletcher, R. J. Dettmar, Krzysztof T. Chyzy, Matthias Hoeft, Anna M. M. Scaife, Cathy Horellou, Volker Heesen, and Astronomy
Subjects: COSMIC-RAY TRANSPORT, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Cosmic ray, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, MASS, 01 natural sciences, STAR-FORMATION, magnetic fields [galaxies], cosmic rays, 0103 physical sciences, PHOTOMETRY, HALOES, NEARBY GALAXIES, IC-10, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, radio continuum: galaxies, COSMIC cancer database, RADIO, 010308 nuclear & particles physics, Star formation, Astronomy and Astrophysics, LOFAR, Escape velocity, Astrophysics - Astrophysics of Galaxies, galaxies [radio continuum], Galaxy, Radio halo, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Irregular galaxy, galaxies: magnetic fields, SKY SURVEY
Abstract: Low-mass galaxies are subject to strong galactic outflows, in which cosmic rays may play an important role, they can be best traced with low-frequency radio continuum observations, which are less affected by spectral ageing. We present a study of the nearby star burst dwarf irregular galaxy IC 10 using observations at 140 MHz with the LOw-Frequency ARray (LOFAR), at 1580 MHz with the Very Large Array (VLA) and at 6200 MHz with the VLA and the 100-m Effelsberg telescope. We find that IC 10 has a low-frequency radio halo, which manifests itself as a second component (thick disc) in the minor axis profiles of the non-thermal radio continuum emission at 140 and 1580 MHz. These profiles are then fitted with 1D cosmic-ray transport models for pure diffusion and advection. We find that a diffusion model fits best, with a diffusion coefficient of $D=(0.4$-$0.8) \times 10^{26}(E/{\rm GeV})^{0.5}~{\rm cm^2\,s^{-1}}$, which is at least an order of magnitude smaller than estimates both from anisotropic diffusion and the diffusion length. In contrast, advection models, which cannot be ruled out due to the mild inclination, while providing poorer fits, result in advection speeds close to the escape velocity of $\approx$$50~\rm km\,s^{-1}$, as expected for a cosmic-ray driven wind. Our favoured model with an accelerating wind provides a self-consistent solution, where the magnetic field is in energy equipartition with both the warm neutral and warm ionized medium with an important contribution from cosmic rays. Consequently, cosmic rays can play a vital role for the launching of galactic winds in the disc--halo interface., Comment: 10 pages, 5 colour figures, 1 table. Accepted by MNRAS
Published: 2018
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40. The widest frequency radio relic spectra: observations from 150 MHz to 30 GHz

Author: Clare Rumsey, M. Kierdorf, Carmen Rodríguez-Gonzálvez, J. M. F. Donnert, Timothy W. Shimwell, Huub Röttgering, Andra Stroe, Matthias Hoeft, Thomas W Jones, Reinout J. van Weeren, Jeremy J. Harwood, and Richard D. E. Saunders
Subjects: Shock wave, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, Arcminute Microkelvin Imager, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, 01 natural sciences, Spectral line, law.invention, Jansky, Telescope, Radio relics, law, Intracluster medium, 0103 physical sciences, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, Astrophysics - Astrophysics of Galaxies, Synchrotron, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics are patches of diffuse synchrotron radio emission that trace shock waves. Relics are thought to form when intra-cluster medium electrons are accelerated by cluster merger induced shock waves through the diffusive shock acceleration mechanism. In this paper, we present observations spanning 150 MHz to 30 GHz of the `Sausage' and `Toothbrush' relics from the Giant Metrewave and Westerbork telescopes, the Karl G. Jansky Very Large Array, the Effelsberg telescope, the Arcminute Microkelvin Imager and Combined Array for Research in Millimeter-wave Astronomy. We detect both relics at 30 GHz, where the previous highest frequency detection was at 16 GHz. The integrated radio spectra of both sources clearly steepen above 2 GHz, at the >6$\sigma$ significance level, supports the spectral steepening previously found in the `Sausage' and the Abell 2256 relic. Our results challenge the widely adopted simple formation mechanism of radio relics and suggest more complicated models have to be developed that, for example, involve re-acceleration of aged seed electrons., Comment: Accepted for publication in MNRAS; 16 pages, 11 figures
Published: 2015
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41. LOFAR discovery of a quiet emission mode in PSR B0823+26

Author: F. Breitling, Gottfried Mann, R. Pizzo, John D. Anderson, Cees Bassa, Sera Markoff, Rene P. Breton, Ashish Asgekar, Charlotte Sobey, E. Jütte, George Heald, Heino Falcke, P. Maat, M. J. Norden, M. A. Garrett, Jean-Mathias Grießmeier, Ph. Zarka, Rebecca McFadden, H. Paas, Ben Stappers, E. de Geus, Sarod Yatawatta, V. I. Kondratiev, D. D. Mulcahy, J. van Leeuwen, S. ter Veen, M. Pilia, M. Pandey-Pommier, Ralph A. M. J. Wijers, A. W. Gunst, J. Sluman, Olaf Wucknitz, H. J. A. Röttgering, Philip Best, Christian Vocks, D. McKay-Bukowski, Michel Tagger, D. Carbone, A. Alexov, Andrew Lyne, Antonia Rowlinson, A. Noutsos, Adam Stewart, Chiara Ferrari, T. E. Hassall, Evan Keane, Patrick Weltevrede, Jason W. T. Hessels, Satyendra Thoudam, S. Duscha, M. Serylak, A. van Duin, G. Pietka, Laura Birzan, Jochen Eislöffel, J. P. Hamaker, Wilfred Frieswijk, C. Toribio, Michael Kramer, D. A. Rafferty, A. G. Polatidis, Arthur Corstanje, A. Nelles, John D. Swinbank, Y. Tang, Anna M. M. Scaife, Martin Bell, N. J. Young, V. N. Pandey, Gerard H. Kuper, Cyril Tasse, J. W. Broderick, H. Munk, John McKean, Marcus Brüggen, Matthias Steinmetz, Annalisa Bonafede, A. Renting, Richard Fallows, R. Vermeulen, Mark J. Bentum, Matthias Hoeft, M. de Vos, Aris Karastergiou, Michael W. Wise, Gianni Bernardi, Jörg R. Hörandel, Rob Fender, Oleg Smirnov, Emanuela Orru, Dominik J. Schwarz, I. M. Avruch, Anna V. Bilous, R. J. van Weeren, Sobey, C., Young, N.J., Hessels, J.W.T., Weltevrede, P., Noutsos, A., Stappers, B.W., Kramer, M., Bassa, C., Lyne, A.G., Kondratiev V.I., null, Hassall, T.E., Keane, E.F., Bilous, A.V., Breton, R.P., Grießmeier, J.M., Karastergiou, A., Pilia, M., Serylak, M., Ter Veen, S., Van Leeuwen, J., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Bell, M.E., Bentum, M.J., Bernardi, G., Best, P., Bĭrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Corstanje, A., Carbone, D., De Geus, E., De Vos, M., Van Duin, A., Duscha, S., Eislöffel, J., Falcke, H., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Gunst, A.W., Hamaker, J.P., Heald, G., Hoeft, M., Hörandel, J., Jütte, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., McKean, J.P., Mulcahy, D.D., Munk, H., Nelles, A., Norden, M.J., Orrù, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pietka, G., Pizzo, R., Polatidis, A.G., Rafferty, D., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A.M.M., Schwarz, D., Sluman, J., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, C., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Yatawatta, S., Zarka, P., Max-Planck-Institut für Radioastronomie (MPIFR), University of Minnesota [Twin Cities] (UMN), University of Minnesota System, University of Amsterdam [Amsterdam] (UvA), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Columbia Astrophysics Laboratory (CAL), Columbia University [New York], Cornell University [New York], Netherlands Institute for Radio Astronomy (ASTRON), Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University [Nijmegen], Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Rhodes University, Grahamstown, Oxford Astrophysics, University of Oxford, Institute for Mathematics Applied to Geoscience, National Center for Atmospheric Research [Boulder] (NCAR), SRON Netherlands Institute for Space Research (SRON), CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), University of Southampton, Medstar Research Institute, Thüringer Landessternwarte Tautenburg (TLS), Institute of Mathematical and Physical Sciences, Département de Géologie, Université de Montréal (UdeM), University Bochum, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Oulu, Center for Information Technology CIT, Université de Groningen, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), Department of Astronomy and Astrophysics [PennState], Pennsylvania State University (Penn State), Penn State System-Penn State System, School of Physics and Astronomy [Southampton], Interactions Son Musique Mouvement, Sciences et Technologies de la Musique et du Son (STMS), Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche et Coordination Acoustique/Musique (IRCAM)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Université Paris-Sud - Paris 11 (UP11), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), SKA South Africa, Ska South Africa, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, We would like to thank R. Karuppusamy for his help with the Effelsberg observations. CF acknowledges financial support by the Agence Nationale de la Recherche through grant ANR-09-JCJC-0001-01., European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), ITA, GBR, FRA, DEU, NLD, Radboud university [Nijmegen], Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), University of Oxford [Oxford], Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Pierre et Marie Curie - Paris 6 (UPMC), Universiteit Leiden [Leiden], École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Harvard University [Cambridge]-Smithsonian Institution, Astronomy, and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: stars, PSR B0823+26-radio telescopes, Astronomy, Astrophysics::High Energy Astrophysical Phenomena, Pulsar planet, FOS: Physical sciences, neutron- pulsars, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, neutron [stars], Pulsar, Millisecond pulsar, Pulsars: individual: PSR B0823+26, individual, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics, Astroparticle physics, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Stars: neutron, Stars, Neutron star, Astrophysics - Solar and Stellar Astrophysics, magnetosphere-pulsars, [SDU]Sciences of the Universe [physics], Space and Planetary Science, QUIET, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Astrophysics - High Energy Astrophysical Phenomena, individual: PSR B0823+26 [pulsars]
Abstract: PSR B0823+26, a 0.53-s radio pulsar, displays a host of emission phenomena over timescales of seconds to (at least) hours, including nulling, subpulse drifting, and mode-changing. Studying pulsars like PSR B0823+26 provides further insight into the relationship between these various emission phenomena and what they might teach us about pulsar magnetospheres. Here we report on the LOFAR discovery that PSR B0823+26 has a weak and sporadically emitting 'quiet' (Q) emission mode that is over 100 times weaker (on average) and has a nulling fraction forty-times greater than that of the more regularly-emitting 'bright' (B) mode. Previously, the pulsar has been undetected in the Q-mode, and was assumed to be nulling continuously. PSR B0823+26 shows a further decrease in average flux just before the transition into the B-mode, and perhaps truly turns off completely at these times. Furthermore, simultaneous observations taken with the LOFAR, Westerbork, Lovell, and Effelsberg telescopes between 110 MHz and 2.7 GHz demonstrate that the transition between the Q-mode and B-mode occurs within one single rotation of the neutron star, and that it is concurrent across the range of frequencies observed., Comment: 15 pages, 8 figures, 2 tables, accepted for publication in MNRAS
Published: 2015
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42. The association of a J-burst with a solar jet

Author: Helmut O. Rucker, Rebecca McFadden, B. Ciardi, J. M. Anderson, H. Munk, J. W. Broderick, O. Wucknitz, H. Paas, E. Juette, W. Reich, Heino Falcke, Matthias Hoeft, Hamish A. S. Reid, Oleg Smirnov, L. Cerrigone, A. G. Polatidis, Philip Best, Emanuela Orrú, Matthias Steinmetz, J. Magdalenic, D. D. Mulcahy, Gottfried Mann, C. Vocks, P. Zarka, V. N. Pandey, Ashish Asgekar, Mark J. Bentum, Gerard H. Kuper, A. Nelles, Annalisa Bonafede, M. Iacobelli, Diana E. Morosan, Dominik J. Schwarz, M. Pandey-Pommier, M. C. Toribio, R. C. Vermeulen, Jochen Eislöffel, Jean-Mathias Griessmeier, M. Tagger, S. ter Veen, A. W. Gunst, S. Duscha, Mario M. Bisi, R. Blaauw, R. J. van Weeren, D. McKay-Bukowski, I. M. Avruch, Peter T. Gallagher, John McKean, Martin Bell, E. de Geus, M. A. Garrett, Richard Fallows, Frank Breitling, Bo Thidé, J. Sluman, Roberto Pizzo, Marcus Brüggen, Satyendra Thoudam, Astronomy, Kapteyn Astronomical Institute, Trinity College Dublin, Netherlands Institute for Radio Astronomy (ASTRON), SUPA School of Physics and Astronomy [Glasgow], University of Glasgow, Leibniz-Institut für Astrophysik Potsdam (AIP), STFC Rutherford Appleton Laboratory (RAL), Science and Technology Facilities Council (STFC), Royal Observatory of Belgium [Brussels] (ROB), Austrian Academy of Sciences (OeAW), Swedish Institute of Space Physics [Uppsala] (IRF), GeoForschungsZentrum - Helmholtz-Zentrum Potsdam (GFZ), Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], CSIRO Astronomy and Space Science, Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Royal Observatory Edinburgh (ROE), University of Edinburgh, Jacobs University [Bremen], Universität Hamburg (UHH), Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Leiden Observatory [Leiden], Universiteit Leiden, Ruhr-Universität Bochum [Bochum], University of Oulu, Radboud University [Nijmegen], Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Max-Planck-Institut für Radioastronomie (MPIFR), Universität Bielefeld, Rhodes University, Grahamstown, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO), Universiteit Leiden [Leiden], Radboud university [Nijmegen], École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and Harvard University [Cambridge]-Smithsonian Institution
Subjects: corona [Sun], 010504 meteorology & atmospheric sciences, Astronomy, particle emission [Sun], Astrophysics, 01 natural sciences, ELECTRON-BEAMS, CORONA, Sun: magnetic, Coronal mass ejection, Astrophysics::Solar and Stellar Astrophysics, GeneralLiterature_REFERENCE(e.g.,dictionaries,encyclopedias,glossaries), 010303 astronomy & astrophysics, Sun: magnetic fields, fields, Physics, Jet (fluid), Solar flare, Sun: radio radiation, Astrophysics::Instrumentation and Methods for Astrophysics, FLARE, Astrophysics - Solar and Stellar Astrophysics, magnetic fields [Sun], Physical Sciences, Physics::Space Physics, Astrophysics::Earth and Planetary Astrophysics, FLUX, DYNAMICS-OBSERVATORY SDO, Field line, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy & Astrophysics, ACCELERATION, Computer Science::Digital Libraries, III BURSTS, Sun: particle emission, 0103 physical sciences, Solar and Stellar Astrophysics (astro-ph.SR), 0105 earth and related environmental sciences, Science & Technology, radio radiation [Sun], [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Sun: corona, Northern Hemisphere, Astronomy and Astrophysics, Magnetic reconnection, LOFAR, Physics::History of Physics, X-RAY JETS, 13. Climate action, Space and Planetary Science, Extreme ultraviolet, RADIO-EMISSION
Abstract: Context. The Sun is an active star that produces large-scale energetic events such as solar flares and coronal mass ejections and numerous smaller-scale events such as solar jets. These events are often associated with accelerated particles that can cause emission at radio wavelengths. The reconfiguration of the solar magnetic field in the corona is believed to be the cause of the majority of solar energetic events and accelerated particles. Aims. Here, we investigate a bright J-burst that was associated with a solar jet and the possible emission mechanism causing these two phenomena. Methods. We used data from the Solar Dynamics Observatory (SDO) to observe a solar jet, and radio data from the Low Frequency Array (LOFAR) and the Nan\c{c}ay Radioheliograph (NRH) to observe a J-burst over a broad frequency range (33-173 MHz) on 9 July 2013 at ~11:06 UT. Results. The J-burst showed fundamental and harmonic components and it was associated with a solar jet observed at extreme ultraviolet wavelengths with SDO. The solar jet occurred at a time and location coincident with the radio burst, in the northern hemisphere, and not inside a group of complex active regions in the southern hemisphere. The jet occurred in the negative polarity region of an area of bipolar plage. Newly emerged positive flux in this region appeared to be the trigger of the jet. Conclusions. Magnetic reconnection between the overlying coronal field lines and the newly emerged positive field lines is most likely the cause of the solar jet. Radio imaging provides a clear association between the jet and the J-burst which shows the path of the accelerated electrons., Comment: 11 pages, 8 figures
Published: 2017
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43. Can cluster merger shocks reproduce the luminosity and shape distribution of radio relics?

Author: Sebastián E. Nuza, Matthias Hoeft, Jakob Gelszinnis, and Gustavo Yepes
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Distribution (number theory), Astrophysics::High Energy Astrophysical Phenomena, NUMERICAL [METHODS], Ciencias Físicas, FOS: Physical sciences, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, NON-THERMAL [RADIATION MECHANISMS], 01 natural sciences, Luminosity, purl.org/becyt/ford/1 [https], Radio relics, 0103 physical sciences, Cluster (physics), 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, Physics, 010308 nuclear & particles physics, Astronomy, Astronomy and Astrophysics, purl.org/becyt/ford/1.3 [https], Astrophysics - Astrophysics of Galaxies, Astronomía, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), CLUSTERS: GENERAL [GALAXIES], LARGE-SCALE STRUCTURE OF UNIVERSE, SHOCK WAVES, CIENCIAS NATURALES Y EXACTAS, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: Radio relics in galaxy clusters are believed to trace merger shock fronts. If cosmological structure formation determines the luminosity, size and shape distributions of radio relics then merger shocks need to be lighted up in a homogeneous way. We investigate if a mock relic sample, obtained from zoomed galaxy cluster simulations, is able to match the properties of relics measured in the NRAO VLA Sky Survey (NVSS). We compile a list of all radio relics known to date and homogeneously measure their parameters in all NVSS images and apply the same procedure to relics in our simulations. Number counts in the mock relic sample increase more steeply towards lower relic flux densities, suggesting an incompleteness of NVSS in this regime. Overall, we find that NVSS and mock samples show similar properties. However, large simulated relics tend to be somewhat smaller and closer to the cluster centre than observed ones. Besides this, the mock sample reproduces very well-known correlations for radio relics, in particular those relating the radio luminosity with the largest linear size and the X-ray luminosity. We show that these correlations are largely governed by the sensitivity of the NVSS observations. Mock relics show a similar orientation with respect to the direction to the cluster centre as the NVSS sample. Moreover, we find that their maximum radio luminosity roughly correlates with cluster mass, although displaying a large scatter. The overall good agreement between NVSS and the mock sample suggests that properties of radio relics are indeed governed by merger shock fronts, emitting in a homogeneous fashion. Our study demonstrates that the combination of mock observations and data from upcoming radio surveys will allow to shed light on both the origin of radio relics and the nature of the intracluster medium., Comment: Replaced to match published version. Minor corrections. References added; 27 pages, 19 figures, 2 tables. Radio relic compilation presented in Table 1. Properties of relic regions identified in NVSS presented in Table 2
Published: 2017

44. Reconciling radio relic observations and simulations: The NVSS sample

Author: Jakob Gelszinnis, Sebastián E. Nuza, and Matthias Hoeft
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), Surface brightness, Population, FOS: Physical sciences, Sample (statistics), Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Surveys, Angular sizes, Acceleration, Physics::Popular Physics, Radio relics, Cluster (physics), Diffusive shock accelerations, education, Konferenzschrift, Physics, education.field_of_study, High Energy Physics::Phenomenology, Intrinsic bias, Astrophysics - Astrophysics of Galaxies, Driving mechanism, Astrophysics of Galaxies (astro-ph.GA), Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The diffusive shock acceleration scenario is usually invoked to explain radio relics, although the detailed driving mechanism is still a matter of debate. Our aim is to constrain models for the origin of radio relics by comparing observed relic samples with simulated ones. Here we present a framework to homogeneously extract the whole sample of known radio relics from NVSS so that it can be used for comparison with cosmological simulations. In this way, we can better handle intrinsic biases in the analysis of the radio relic population. In addition, we show some properties of the resulting NVSS sample relics such as the correlation between relic shape and orientation with respect to the cluster. Also, we briefly discuss the typical relic surface brightness and its relation to projected cluster distance and relic angular sizes., 4 pages, 2 figures. Proceedings of "The many facets of extragalactic radio surveys: towards new scientific challenges" (EXTRA-RADSUR2015). 20-23 October 2015. Bologna, Italy
Published: 2017

45. The LOFAR Two-metre Sky Survey: I. Survey description and preliminary data release

Author: Jeremy J. Harwood, Matthias Steinmetz, W. van Driel, Leah K. Morabito, Emanuela Orru, Magdalena Kunert-Bajraszewska, D. A. Rafferty, Isabella Prandoni, A. Horneffer, Huub Röttgering, R. J. van Weeren, Adam Deller, Subhash C. Mandal, J. Sabater, G. Calistro Rivera, M. Sipior, Daniel J. Smith, Frank P. Israel, Aleksandar Shulevski, John McKean, Marijke Haverkorn, D. Engels, Krzysztof T. Chyzy, Chiara Ferrari, P. van der Werf, Philip Best, J. B. R. Oonk, A. Drabent, Elizabeth K. Mahony, Raffaella Morganti, Marisa Brienza, Timothy W. Shimwell, Michael W. Wise, Annalisa Bonafede, Martin J. Hardcastle, Rainer Beck, S. S. Sridhar, Marcus Brüggen, Neal Jackson, Dominik J. Schwarz, M. A. Garrett, Cathy Horellou, Matthias Hoeft, J. A. Zensus, Gianfranco Brunetti, N. R. Mohan, George K. Miley, Andra Stroe, John Conway, Anna D. Kapińska, E. Retana-Montenegro, D. J. McKay, A. O. Clarke, I. van Bemmel, Glenn J. White, George Heald, Volker Heesen, Heino Falcke, Matt J. Jarvis, F. de Gasperin, Huib Intema, D. N. Hoang, Cyril Tasse, R. Pizzo, Eskil Varenius, S. Fröhlich, A. P. Mechev, D. Cseh, Wendy L. Williams, Rossella Cassano, Jonathan T. L. Zwart, T. J. Dijkema, Leiden Observatory [Leiden], Universiteit Leiden, Institute for Astronomy [Edinburgh] (IfA), University of Edinburgh, Centre for Astrophysics Research, University of Hertfordshire [Hatfield] (UH), Netherlands Institute for Radio Astronomy (ASTRON), Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Max-Planck-Institut für Radioastronomie (MPIFR), Galaxies, Etoiles, Physique, Instrumentation (GEPI), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, Istituto di Radioastronomia [Bologna] (IRA), Istituto Nazionale di Astrofisica (INAF), Astronomical Observatory [Kraków], Uniwersytet Jagielloński w Krakowie = Jagiellonian University (UJ), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], Radboud University [Nijmegen], Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Oxford Astrophysics, University of Oxford, Department of Physics and Astronomy [Milton Keynes], The Open University [Milton Keynes] (OU), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Thüringer Landessternwarte Tautenburg (TLS), Unité Scientifique de la Station de Nançay (USN), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Ruhr-Universität Bochum [Bochum], School of Physics and Astronomy [Southampton], University of Southampton, Joint Institute for VLBI in Europe (JIVE ERIC), Department of Earth and Space Sciences [Göteborg], The University of Western Australia (UWA), Torun Centre for Astronomy (TCfA), Nicolaus Copernicus University [Toruń], University of Oulu, National Centre for Radio Astrophysics [Pune] (NCRA), Tata Institute for Fundamental Research (TIFR), Universität Bielefeld, Leibniz-Institut für Astrophysik Potsdam (AIP), European Southern Observatory (ESO), University of the Western Cape (UWC), European Project: 320745,EC:FP7:ERC,ERC-2012-ADG_20120216,RADIOLIFE(2013), Astronomy, Kapteyn Astronomical Institute, Universiteit Leiden [Leiden], Harvard University [Cambridge]-Smithsonian Institution, Radboud university [Nijmegen], University of Oxford [Oxford], Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), University of the Western Cape, High Energy Astrophys. & Astropart. Phys (API, FNWI), PSL Research University (PSL)-PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Smithsonian Institution-Harvard University [Cambridge], Istituto di Radioastronomia INAF, Jagiellonian University [Krakow] (UJ), Onsala Space Observatory, Istituto di Radioastronomia (IRA), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO)-Observatoire de Paris, PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), and Tata Institute of Fundamental Research [Bombay] (TIFR)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010504 meteorology & atmospheric sciences, media_common.quotation_subject, Astronomy, radio continuum: general, FOS: Physical sciences, techniques: image processing, 01 natural sciences, Declination, Spectral line, RADIO RECOMBINATION LINES, techniques image processing, surveys, CALIBRATOR SURVEY, 0103 physical sciences, Calibration, radio-continuum, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, 0105 earth and related environmental sciences, Remote sensing, media_common, [SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph], image processing [techniques], QUASAR SURVEY, Astronomy and Astrophysics, HERSCHEL-ATLAS, LOFAR, 1ST SURVEY, Galaxy, WIDE-FIELD, Space and Planetary Science, Sky, LUMINOSITY FUNCTION, general, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, general [radio continuum], CHANDRA OBSERVATIONS, Astrophysics - Instrumentation and Methods for Astrophysics, Right ascension, FOLLOW-UP, GALAXY CLUSTERS, surveys – catalogs – radio continuum: general – techniques: image processing, Geology, Noise (radio), catalogs, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The LOFAR Two-metre Sky Survey (LoTSS) is a deep 120-168 MHz imaging survey that will eventually cover the entire Northern sky. Each of the 3170 pointings will be observed for 8 hrs, which, at most declinations, is sufficient to produce ~5arcsec resolution images with a sensitivity of ~0.1mJy/beam and accomplish the main scientific aims of the survey which are to explore the formation and evolution of massive black holes, galaxies, clusters of galaxies and large-scale structure. Due to the compact core and long baselines of LOFAR, the images provide excellent sensitivity to both highly extended and compact emission. For legacy value, the data are archived at high spectral and time resolution to facilitate subarcsecond imaging and spectral line studies. In this paper we provide an overview of the LoTSS. We outline the survey strategy, the observational status, the current calibration techniques, a preliminary data release, and the anticipated scientific impact. The preliminary images that we have released were created using a fully-automated but direction-independent calibration strategy and are significantly more sensitive than those produced by any existing large-area low-frequency survey. In excess of 44,000 sources are detected in the images that have a resolution of 25arcsec, typical noise levels of less than 0.5 mJy/beam, and cover an area of over 350 square degrees in the region of the HETDEX Spring Field (right ascension 10h45m00s to 15h30m00s and declination 45d00m00s to 57d00m00s)., Comment: 23 pages, 15 figures, 3 tables, accepted for publication in A&A
Published: 2017
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46. A LOFAR detection of the low mass young star T Tau at 149 MHz

Author: Adam Stewart, M. Pietka, Stephane Corbel, Tom Ray, Anna M. M. Scaife, A. Drabent, Alexander J. van der Horst, Matthias Hoeft, P. Zarka, Jean-Mathias Greißmeier, Colm P. Coughlan, Martin Bell, Rachael E. Ainsworth, Joeri van Leeuwen, Jochen Eislöffel, Ralph A. M. J. Wijers, J. W. Broderick, Sera Markoff, Dublin Institute for Advanced Studies (DIAS), Thüringer Landessternwarte Tautenburg (TLS), School of Physics and Astronomy [Southampton], University of Southampton, Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, Unité Scientifique de la Station de Nançay (USN), Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), Astrophysique Interprétation Modélisation (AIM (UMR_7158 / UMR_E_9005 / UM_112)), Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris Diderot - Paris 7 (UPD7), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Oxford Astrophysics, University of Oxford [Oxford], Laboratory for Atmospheric and Space Physics [Boulder] (LASP), University of Colorado [Boulder], Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), ERC-2012-StG-307215 LODESTONE, European Project: 307215,EC:FP7:ERC,ERC-2012-StG_20111012,LODESTONE(2013), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Astrophysique Interprétation Modélisation (AIM (UMR7158 / UMR_E_9005 / UM_112)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), University of Oxford, High Energy Astrophys. & Astropart. Phys (API, FNWI), Université d'Orléans (UO)-Observatoire des Sciences de l'Univers en région Centre (OSUC), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, PSL Research University (PSL)-Centre National de la Recherche Scientifique (CNRS), PSL Research University (PSL)-PSL Research University (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Centre National de la Recherche Scientifique (CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Observatoire de Paris, and PSL Research University (PSL)-PSL Research University (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)
Subjects: Electron density, 010504 meteorology & atmospheric sciences, Young stellar object, Astrophysics::High Energy Astrophysical Phenomena, Flux, FOS: Physical sciences, Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astronomy & Astrophysics, 7. Clean energy, 01 natural sciences, 0103 physical sciences, individual (T Tauri) [stars], Protostar, pre-main sequence [stars], 010303 astronomy & astrophysics, stars [radio continuum], Astrophysics::Galaxy Astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), protostars [stars], 0105 earth and related environmental sciences, Physics, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Astronomy and Astrophysics, LOFAR, Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), thermal [radiation mechanisms], Content (measure theory), Spectral energy distribution, Low Mass
Abstract: Radio observations of young stellar objects (YSOs) enable the study of ionised plasma outflows from young protostars via their free-free radiation. Previous studies of the low-mass young system T Tau have used radio observations to model the spectrum and estimate important physical properties of the associated ionised plasma (local electron density, ionised gas content and emission measure). However, without an indication of the low-frequency turnover in the free-free spectrum, these properties remain difficult to constrain. This paper presents the detection of T Tau at 149 MHz with the Low Frequency Array (LOFAR) - the first time a YSO has been observed at such low frequencies. The recovered total flux indicates that the free-free spectrum may be turning over near 149 MHz. The spectral energy distribution is fitted and yields improved constraints on local electron density ($(7.2 \pm 2.1)\times10^{3}$ cm$^{-3}$), ionised gas mass ($(1.0 \pm 1.8)\times10^{-6}$ M$_{\odot}$) and emission measure ($(1.67 \pm 0.14)\times10^5$ pc cm$^{-6}$)., Comment: 10 pages, accepted for publication in ApJ
Published: 2017
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47. LOFAR discovery of an ultra-steep radio halo and giant head-tail radio galaxy in Abell 1132

Author: F. de Gasperin, D. Rafferty, Annalisa Bonafede, F. Savini, Timothy W. Shimwell, G. Brunetti, Renato Teofilo Giuseppe Morganti, A. O. Clarke, Huib Intema, A. P. Mechev, S. Mandal, Elizabeth K. Mahony, A. Wilber, Marcus Brüggen, Isabella Prandoni, Felipe Andrade-Santos, Huub Röttgering, R. J. van Weeren, Matthias Hoeft, Astronomy, Wilber, A., Brüggen, M., Bonafede, A., Savini, F., Shimwell, T., van Weeren, R.J., Rafferty, D., Mechev, A.P., Intema, H., Andrade-Santos, F., Clarke, A.O., Mahony, E.K., Morganti, R., Prandoni, I., Brunetti, G., Röttgering, H., Mandal, S., de Gasperin, F., and Hoeft, M.
Subjects: SAMPLE, galaxies: clusters: intracluster medium, Radio galaxy, COMA CLUSTER, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, COSMIC-RAY PROTONS, Astrophysics::Cosmology and Extragalactic Astrophysics, ACCELERATION, SCALING RELATIONS, 01 natural sciences, Radio continuum: galaxie, Radio telescope, X-shaped radio galaxy, 0103 physical sciences, HADRONIC MODELS, 010303 astronomy & astrophysics, Galaxy cluster, Astrophysics::Galaxy Astrophysics, Physics, radio continuum: galaxies, REACCELERATION, 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, galaxies: clusters: individual: Abell 1132, GAMMA-RAY, Radio halo, Space and Planetary Science, galaxies: clusters: general, Astrophysics of Galaxies (astro-ph.GA), Elliptical galaxy, Halo, SKY SURVEY, EMISSION
Abstract: LOFAR observations at 144 MHz have revealed large-scale radio sources in the unrelaxed galaxy cluster Abell 1132. The cluster hosts diffuse radio emission on scales of $\sim$650 kpc near the cluster center and a head-tail (HT) radio galaxy, extending up to 1 Mpc, South of the cluster center. The central diffuse radio emission is not seen in NVSS, FIRST, WENSS, nor in C & D array VLA observations at 1.4 GHz, but is detected in our follow-up GMRT observations at 325 MHz. Using LOFAR and GMRT data, we determine the spectral index of the central diffuse emission to be $\alpha=-1.75\pm0.19$ ($S\propto\nu^{\alpha}$). We classify this emission as an ultra-steep spectrum radio halo and discuss the possible implications for the physical origin of radio halos. The HT radio galaxy shows narrow, collimated emission extending up to 1 Mpc and another 300 kpc of more diffuse, disturbed emission, giving a full projected linear size of 1.3 Mpc - classifying it as a giant radio galaxy (GRG) and making it the longest HT found to date. The head of the GRG coincides with an elliptical galaxy (SDSS J105851.01$+$564308.5) belonging to Abell 1132. In our LOFAR image, there appears to be a connection between the radio halo and the GRG. The turbulence that may have produced the halo may have also affected the tail of the GRG. In turn, the GRG may have provided seed electrons for the radio halo., Comment: Accepted to MNRAS, 12 pages, 8 figures
Published: 2017
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48. Challenges to our understanding of radio relics: X-ray observations of the Toothbrush cluster

Author: H. J. A. Röttgering, Matthias Hoeft, Judith H. Croston, Marcus Brüggen, R. J. van Weeren, and Georgiana A. Ogrean
Subjects: Shock wave, Physics, Spectral index, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Radio spectrum, Radio relics, Radio halo, X-shaped radio galaxy, Space and Planetary Science, Surface brightness, Astrophysics::Galaxy Astrophysics, Galaxy cluster, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three radio relics and a giant radio halo. The northern relic, the Toothbrush, is 1.9-Mpc long and has an unusual linear morphology. According to simple diffusive shock acceleration theory, its radio spectral index indicates a Mach number of 3.3-4.6. Here, we present results from a deep XMM-Newton observation of the cluster. We observe two distinct cluster cores that have survived the merger. The presence of three shocks at or near the locations of the radio relics is confirmed by density and temperature discontinuities. However, the observation poses several puzzles that challenge our understanding of radio relics: (i) at the Toothbrush, the shock Mach number is not larger than 2, in apparent conflict with the shock strength predicted from the radio spectrum; (ii) at the Toothbrush, the shock front is, in part, spatially offset from the radio emission; (iii) at the eastern relic, we detect a temperature jump corresponding to a Mach number of approximately 2.5, but there is no associated surface brightness discontinuity. We discuss possible explanations for these findings., Comment: 14 pages, 15 figures; submitted to MNRAS
Published: 2013
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49. XMM–Newton observations of the merging galaxy cluster CIZA J2242.8+5301

Author: Judith H. Croston, H. J. A. Röttgering, Matthias Hoeft, Aurora Simionescu, Georgiana A. Ogrean, R. J. van Weeren, and Marcus Brüggen
Subjects: Shock wave, Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), Shock (fluid dynamics), Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astronomy, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Classification of discontinuities, Galaxy, Radio halo, Space and Planetary Science, Intracluster medium, Cluster (physics), Astrophysics::Galaxy Astrophysics, Galaxy cluster, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract: We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301 using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long, ~50-kpc wide radio relic that has been nicknamed the "Sausage". A smaller, more irregular counter-relic is also present, along with a faint giant radio halo. We analysed the distribution of the ICM physical properties, and searched for shocks by trying to identify density and temperature discontinuities. East of the southern relic, we find evidence of shock compression corresponding to a Mach number of 1.3, and speculate that the shock extends beyond the length of the radio structure. The ICM temperature increases at the northern relic. More puzzling, we find a "wall" of hot gas east of the cluster centre. A partial elliptical ring of hot plasma appears to be present around the merger. While radio observations and numerical simulations predict a simple merger geometry, the X-ray results point towards a more complex merger scenario., Extensively revised and expanded, with 18 pages and 17 figures
Published: 2013
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50. Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Author: Y. Tang, Anna M. M. Scaife, Steve Rawlings, Aris Karastergiou, Michael W. Wise, Harvey Butcher, B. Ciardi, S. Duscha, V. N. Pandey, Gianni Bernardi, John McKean, Charlotte Sobey, Emanuela Orrú, Chiara Ferrari, M. Kuniyoshi, H. Munk, Marcus Brüggen, Michael Kramer, Cyril Tasse, J. W. Broderick, E. de Geus, Ashish Asgekar, Jason W. T. Hessels, F. de Gasperin, Matthias Hoeft, George Heald, L. Kuiper, A. P. Schoenmakers, P. Maat, R. H. van de Brink, Sera Markoff, Dipanjan Mitra, Philip Best, G. Wright, Ralph A. M. J. Wijers, J. de Plaa, Heino Falcke, V. I. Kondratiev, Rahul Basu, A. Noutsos, T. Coenen, Benjamin Stappers, Michel Tagger, Frank Breitling, Giulia Macario, Rob Fender, Rene C. Vermeulen, Michael R. Bell, F. Batejat, A. Alexov, Marco Iacobelli, H. Paas, Sarod Yatawatta, Patrick Weltevrede, Tim Hassall, R. J. van Weeren, W. Reich, M. Pilia, Laura Birzan, W. Hermsen, Evan Keane, Aleksandar Shulevski, Mark J. Bentum, M. Serylak, Martin Bell, Annalisa Bonafede, J. van Leeuwen, A. Horneffer, Jochen Eislöffel, Maaijke Mevius, H. J. A. Röttgering, A. G. Polatidis, R. Morganti, I. M. Avruch, S. ter Veen, A. W. Gunst, Olaf Wucknitz, Matthias Steinmetz, M. Pandey-Pommier, K. Zagkouris, J. Sluman, Roberto Pizzo, Jean-Mathias Grießmeier, G. Kuper, Philippe Zarka, Joanna M. Rankin, M. A. Garrett, James Miller-Jones, Wilfred Frieswijk, Hermsen, W., Hessels, J.W.T., Kuiper, L., Van Leeuwen, J., Mitra, D., De Plaa, J., Rankin, J.M., Stappers, B.W., Wright, G.A.E., Basu, R., Alexov, A., Coenen, T., Grießmeier, J.-M., Hassall, T.E., Karastergiou, A., Keane, E., Kondratiev, V.I., Kramer, M., Kuniyoshi, M., Noutsos, A., Serylak, M., Pilia, M., Sobey, C., Weltevrede, P., Zagkouris, K., Asgekar, A., Avruch, I.M., Batejat, F., Bell, M.E., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H.R., Ciardi, B., Duscha, S., Eislöffel, J., Falcke, H., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., De Gasperin, F., De Geus, E., Gunst, A.W., Heald, G., Hoeft, M., Horneffer, A., Iacobelli, M., Kuper, G., Maat, P., Macario, G., Markoff, S., McKean, J.P., Mevius, M., Miller-Jones, J.C.A., Morganti, R., Munk, H., Orrú, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A.G., Rawlings, S., Reich, W., Röttgering, H., Scaife, A.M.M., Schoenmakers, A., Shulevski, A., Sluman, J., Steinmetz, M., Tagger, M., Tang, Y., Tasse, C., Ter Veen, S., Vermeulen, R., Van De Brink, R.H., Van Weeren, R.J., Wijers, R.A.M.J., Wise, M.W., Wucknitz, O., Yatawatta, S., Zarka, P., SRON Netherlands Institute for Space Research (SRON), University of Amsterdam [Amsterdam] (UvA), National Centre for Radio Astrophysics [Pune] (NCRA), Tata Institute for Fundamental Research (TIFR), University of Vermont [Burlington], Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Astronomy Centre, University of Sussex, Space Telescope Science Institute (STSci), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Unité Scientifique de la Station de Nançay (USN), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Oxford Astrophysics, University of Oxford, Centre for Astrophysics and Supercomputing, Swinburne University of Technology [Melbourne], Netherlands Institute for Radio Astronomy (ASTRON), Max-Planck-Institut für Radioastronomie (MPIFR), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], University of Southampton, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, University of Edinburgh, Leiden Observatory [Leiden], Universiteit Leiden, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), Radboud University [Nijmegen], Joseph Louis LAGRANGE (LAGRANGE), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Hamburger Sternwarte/Hamburg Observatory, Universität Hamburg (UHH), Medstar Research Institute, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Center for Information Technology CIT, Université de Groningen, Centre de Recherche Astrophysique de Lyon (CRAL), École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), National Radio Astronomy Observatory [Charlottesville] (NRAO), National Radio Astronomy Observatory (NRAO), School of Physics and Astronomy [Southampton], SKA South Africa, Ska South Africa, Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, ANR-09-JCJC-0001,OPALES(2009), Kapteyn Astronomical Institute, Astronomy, Centre National de la Recherche Scientifique (CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Université d'Orléans (UO), University of Oxford [Oxford], Harvard University [Cambridge]-Smithsonian Institution, Universiteit Leiden [Leiden], Radboud university [Nijmegen], Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), École normale supérieure - Lyon (ENS Lyon)-Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), and High Energy Astrophys. & Astropart. Phys (API, FNWI)
Subjects: Electromagnetic field, POLARIZATION, Electromagnetic spectrum, Astrophysics::High Energy Astrophysical Phenomena, Astronomy, FOS: Physical sciences, Magnetosphere, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, EMPIRICAL-THEORY, 01 natural sciences, Binary pulsar, Pulsar, Millisecond pulsar, 0103 physical sciences, 010306 general physics, XMM-NEWTON OBSERVATIONS, 010303 astronomy & astrophysics, Astrophysics::Galaxy Astrophysics, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, DRIFTING SUBPULSES, Multidisciplinary, B0943+10, Polarization (waves), GAMMA-RAY, [SDU]Sciences of the Universe [physics], 13. Climate action, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, RADIATION, EMISSION, Astrophysics - High Energy Astrophysical Phenomena, PHOTON IMAGING CAMERA, POWERED PULSARS, Radio wave
Abstract: Pulsars emit low-frequency radio waves through to high-energy gamma-rays that are generated anywhere from the surface out to the edges of the magnetosphere. Detecting correlated mode changes in the multi-wavelength emission is therefore key to understanding the physical relationship between these emission sites. Through simultaneous observations, we have detected synchronous switching in the radio and X-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio 'bright' mode, the X-rays show only an un-pulsed, non-thermal component. Conversely, when the pulsar is in a radio 'quiet' mode, the X-ray luminosity more than doubles and a 100%-pulsed thermal component is observed along with the non-thermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories., Paper published in Science including supplementary material
Published: 2013
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