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51. 'An X-Raydio Switcheroo' – The detection of correlated mode changes in radio and X-ray

Author

W. Hermsen, Joanna M. Rankin, Ben Stappers, Lucien Kuiper, Jason W. T. Hessels, Joeri van Leeuwen, Geoff Wright, and Dipanjan Mitra

Subjects
Optics, Materials science, Space and Planetary Science, business.industry, Astrophysics::High Energy Astrophysical Phenomena, Mode (statistics), X-ray, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, business
Abstract

We present high-sensitivity XMM/LOFAR observations that show for the first time that mode switching extends from radio to X-ray. In pulsar B0943+10, the known changes in radio profile and drift rate are confidently tied to simultaneous changes in X-ray emission.In mode switching, seen in many pulsars, profile and subpulse-drift behavior change almost instantaneously. The mechanism for these drastic changes, or for the bi-stable emission behavior, is not understood; while even for the basic emission mechanism different families of theories (e.g. vacuum gap, or space-charge limited flow models) exist.To discriminate between such models, we carried out a campaign of 42 hours of simultaneous LOFAR/XMM-Newton observations on PSR B0943+10. Through LOFAR's unparalleled low-frequency sensitivity, mode changes were pinpointed to 10-second accuracy. XMM X-ray photons were next separated by the two radio modes. We discovered large modal differences in the X-ray pulsations, flux, and spectral shapes: in the radio-bright mode, no X-ray pulsations are detected – but in the radio-quiet mode, B0943+10 is strongly pulsating in X-ray.

Published
2012
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52. A search for radio pulsations from neutron star companions of four subdwarf B stars

Author

Joeri van Leeuwen, Thijs Coenen, and Ingrid H. Stairs

Subjects
Physics, 010308 nuclear & particles physics, Astrophysics::High Energy Astrophysical Phenomena, Green Bank Telescope, FOS: Physical sciences, Flux, Astronomy and Astrophysics, Astrophysics::Cosmology and Extragalactic Astrophysics, Astrophysics, Astrophysics - Astrophysics of Galaxies, 01 natural sciences, Subdwarf, Orbit, Stars, Neutron star, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, Astrophysics of Galaxies (astro-ph.GA), 0103 physical sciences, Astrophysics::Solar and Stellar Astrophysics, Astrophysics::Earth and Planetary Astrophysics, Spectroscopy, 010303 astronomy & astrophysics, Solar and Stellar Astrophysics (astro-ph.SR), Astrophysics::Galaxy Astrophysics
Abstract

We searched for radio pulsations from the potential neutron star binary companions to subdwarf B stars HE 0532-4503, HE 0929-0424, TON S 183 and PG 1232-136. Optical spectroscopy of these subdwarfs has indicated they orbit a companion in the neutron star mass range. These companions are thought to play an important role in the poorly understood formation of subdwarf B stars. Using the Green Bank Telescope we searched down to mean flux densities as low as 0.2 mJy, but no pulsed emission was found. We discuss the implications for each system., Accepted for publication in A&A, 4 pages, 1 figure

Published
2011
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53. ERRATUM: 'THE ALLEN TELESCOPE ARRAY TWENTY-CENTIMETER SURVEY—A 690 DEG2, 12 EPOCH RADIO DATA SET. I. CATALOG AND LONG-DURATION TRANSIENT STATISTICS' (2010, ApJ, 719, 45)

Author

Dan Werthimer, Jack Welch, Peter K. G. Williams, Calvin Cheng, Shannon Atkinson, Garrett K. Keating, Dave MacMahon, John Lugten, Artyom Vitouchkine, Douglas Thornton, Ken Smolek, Susanne Jorgensen, T. T. Helfer, Rob Ackermann, Tucker Bradford, G. Engargiola, Ed Fields, William C. Barott, Peter Backus, James R. Forster, John Dreher, Karen Randall, Leo Blitz, Amber Bauermeister, David Whysong, Tom Pierson, Melvyn Wright, Chat Hull, Joeri van Leeuwen, Casey J. Law, G. R. Harp, John Ross, Andrew Siemion, Tom Kilsdonk, Matt Dexter, Chris Cork, Steve Croft, Matt Fleming, Geoffrey C. Bower, Lynn Urry, Jane Jordan, Dave DeBoer, Peter L. McMahon, Seth Shostak, M. M. Davis, Don Backer, Oren Milgrome, Niklas Wadefalk, Douglas C.-J. Bock, Colby Gutierrez-Kraybill, and Jill Tarter

Subjects
Data set, Physics, Centimeter, Space and Planetary Science, Epoch (reference date), Astronomy, Astronomy and Astrophysics, Transient (computer programming), Astrophysics, Short duration, Allen Telescope Array
Published
2010
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55. VOEvent Standard for Fast Radio Bursts

Author

Petroff, Emily, Houben, Leon, Bannister, Keith, Burke-Spolaor, Sarah, Cordes, Jim, Falcke, Heino, Haren, Ronald, Karastergiou, Aris, Kramer, Michael, Law, Casey, Joeri van Leeuwen, Lorimer, Duncan, Martinez-Rubi, Oscar, Rachen, Jörg, Spitler, Laura, and Weltman, Amanda

Subjects
FOS: Physical sciences, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), astro-ph.IM
Abstract

Fast radio bursts are a new class of transient radio phenomena currently detected as millisecond radio pulses with very high dispersion measures. As new radio surveys begin searching for FRBs a large population is expected to be detected in real-time, triggering a range of multi-wavelength and multi-messenger telescopes to search for repeating bursts and/or associated emission. Here we propose a method for disseminating FRB triggers using Virtual Observatory Events (VOEvents). This format was developed and is used successfully for transient alerts across the electromagnetic spectrum and for multi-messenger signals such as gravitational waves. In this paper we outline a proposed VOEvent standard for FRBs that includes the essential parameters of the event and where these parameters should be specified within the structure of the event. An additional advantage to the use of VOEvents for FRBs is that the events can automatically be ingested into the FRB Catalogue (FRBCAT) enabling real-time updates for public use. We welcome feedback from the community on the proposed standard outlined below and encourage those interested to join the nascent working group forming around this topic., 11 pages, 2 figures, parameter definition table in appendix

56. Magnetic Field Decay, or Just Period-Dependent Beaming?

Author

Joeri van Leeuwen and Frank Verbunt

Subjects
Physics, 010504 meteorology & atmospheric sciences, Field (physics), Period (periodic table), Astrophysics::High Energy Astrophysical Phenomena, Astrophysics (astro-ph), FOS: Physical sciences, Astronomy, Astrophysics, Magnetar, 01 natural sciences, Magnetic field, Neutron star, Pulsar, 0103 physical sciences, 010303 astronomy & astrophysics, 0105 earth and related environmental sciences
Abstract

Several recent papers conclude that radio-pulsar magnetic fields decay on a time-scale of 10 Myr, apparently contradicting earlier results. We have implemented the methods of these papers in our code and show that this preference for rapid field decay is caused by the assumption that the beaming fraction does not depend on the period. When we do include this dependence, we find that the observed pulsar properties are reproduced best when the modelled field does not decay. When we assume that magnetic fields of new-born neutron stars are from a distribution sufficiently wide to explain magnetars, the magnetic field and period distributions we predict for radio are pulsars wider than observed. Finally we find that the observed velocities overestimate the intrinsic velocity distribution., Comment: 4 pages, 2 figures. To appear in "Young Neutron Stars and Their Environments" (IAU Symposium 218, ASP Conference Proceedings), eds F. Camilo and B. M. Gaensler

57. Detection of a bright burst from FRB 121102 with Apertif at the Westerbork Synthesis Radio Telescope

Author

Oostrum, L. C., Joeri van Leeuwen, Attema, J., Cappellen, W., Connor, L., Hut, B., Maan, Y., Oosterloo, T. A., Petroff, E., Schuur, D., Sclocco, A., Verheijen, M. A. W., High Energy Astrophys. & Astropart. Phys (API, FNWI), API Other Research (FNWI), and Astronomy

Subjects
Transient, Fast Radio Burst
Abstract

We observed the repeating FRB 121102 (Spitler et al. 2016) while commissioning the Apertif Radio Transient System (ARTS; van Leeuwen 2014) on the Westerbork Synthesis Radio Telescope.

58. The Radio Sky on Short Timescales with LOFAR: Pulsars and Fast Transients

Author

Hessels, J. W. T., Stappers, B. W., Joeri van Leeuwen, and LOFAR

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, Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

LOFAR, the "low-frequency array", will be one of the first in a new generation of radio telescopes and Square Kilometer Array (SKA) pathfinders that are highly flexible in capability because they are largely software driven. LOFAR will not only open up a mostly unexplored spectral window, the lowest frequency radio light observable from the Earth's surface, but it will also be an unprecented tool with which to monitor the transient radio sky over a large field of view and down to timescales of milliseconds or less. Here we discuss LOFAR's current and upcoming capabilities for observing fast transients and pulsars, and briefly present recent commissioning observations of known pulsars., Comment: 6 pages, 1 figure, to appear in the proceedings of "The Low-Frequency Radio Universe", eds. D.J. Saikia, D. Green, Y. Gupta, and T. Venturi

59. Real-time searches for fast transients with Apertif and LOFAR

Author

Joeri van Leeuwen and Yogesh Maan

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Physics, Cosmology and Nongalactic Astrophysics (astro-ph.CO), 010308 nuclear & particles physics, Fast radio burst, Phased array, FOS: Physical sciences, Astronomy, Field of view, LOFAR, 01 natural sciences, law.invention, Radio telescope, Telescope, Pulsar, law, 0103 physical sciences, Time domain, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - High Energy Astrophysical Phenomena, Instrumentation and Methods for Astrophysics (astro-ph.IM), 010303 astronomy & astrophysics, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

With the installation of a new phased array system called Apertif, the instantaneous field of view of the Westerbork Synthesis Radio Telescope (WSRT) has increased to 8.7$\,$deg$^2$. This system has turned the WSRT in to an highly effective telescope to conduct Fast Radio Burst (FRB) and pulsar surveys. To exploit this advantage, an advanced and real-time backend, called the Apertif Radio Transient System (ARTS), is being developed and commissioned at the WSRT. In addition to the real-time detection of FRBs, ARTS will localize the events to about 1/2600 of the field of view --- essential information for identifying the nature of FRBs. ARTS will also trigger real-time follow up with LOFAR of newly detected FRBs, to achieve localization at arcsecond precision. We review the upcoming time-domain surveys with Apertif, and present the current status of the ongoing commissioning of the time domain capabilities of Apertif., Comment: 4 pages, 2 figures; to appear in proceedings of URSI GASS 2017

60. Proceedings of IAU Symposium 291 'Neutron Stars and Pulsars: Challenges and Opportunities after 80 years'

Author

Joeri van Leeuwen

Subjects
High Energy Astrophysical Phenomena (astro-ph.HE), Astrophysics - Solar and Stellar Astrophysics, Astrophysics of Galaxies (astro-ph.GA), FOS: Physical sciences, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Solar and Stellar Astrophysics (astro-ph.SR)
Abstract

These are the Proceedings of IAU Symposium 291, held 20-24 August 2012, in Beijing, China., Comment: An index of the 68 associated contribution preprints. For a PDF preprint of the complete volume, see http://www.pulsarastronomy.net/IAUS291/proceedings/

61. Two Pulsar Discoveries from the Einstein@Home Distributed Computing Project

Author

Deneva, Julia S., Knispel, B., Allen, B., Cordes, J., Bogdanov, S., Brazier, A., Bhat, R., Camilo, F., Chatterjee, S., Crawford, F., Desvignes, G., Freire, P., Hessels, J., Jenet, F., Kaspi, V., Kramer, M., Lazarus, P., Lorimer, D., Joeri van Leeuwen, Lyne, A., Mclaughlin, M., Nice, D., Ransom, S., Siemens, X., Stairs, I., Stappers, B., and Stovall, K.

62. The Allen telescope array: The first widefield, panchromatic, snapshot radio camera

Author

Joeri van Leeuwen, Leo Blitz, Douglas Bock, Don Backer, Amber Bauermeister, Geoffrey C. Bower, Calvin Cheng, Steve D. Croft, Matt Dexter, Greg Engargiola, Ed Fields, Rick Forster, Colby Gutierrez-Kraybill, Carl Heiles, Tamara Helfer, Susan Jorgensen, Garrett Keating, Casey Law, John Lugten, Dave MacMahon, Oren Milgrome, Douglas Thornton, Lynn Urry, Jack Welch, Dan Werthimer, Peter Williams, Melvin Wright, Robert Ackermann, Shannon Atkinson, Peter Backus, William Barott, Tucker Bradford, Michael Davis, Dave DeBoer, John Dreher, Gerry Harp, Jane Jordan, Tom Kilsdonk, Tom Pierson, Karen Randall, John Ross, Seth Shostak, and Jill Tarter

Subjects
Physics, Astrophysics::High Energy Astrophysical Phenomena, media_common.quotation_subject, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy, Astrophysics::Cosmology and Extragalactic Astrophysics, law.invention, Allen Telescope Array, Panchromatic film, Telescope, Primary mirror, Radio observatory, law, Sky, Snapshot (computer storage), Astrophysics::Galaxy Astrophysics, media_common, Remote sensing
Abstract

The first 42 elements of the Allen Telescope Array (ATA-42) are beginning to deliver data at the Hat Creek Radio Observatory in Northern California. Scientists and engineers are actively exploiting all of the flexibility designed into this innovative instrument for simultaneously conducting panoramic surveys of the astrophysical sky. The fundamental scientific program of this new telescope is varied and exciting; we here discuss some of the first astronomical results.

64. A Search for Pulsars in Steep Spectrum Radio Sources.

Author

Yogesh Maan, Cees Bassa, Joeri van Leeuwen, M. A. Krishnakumar, and Bhal Chandra Joshi

Subjects
PULSARS, RADIO sources (Astronomy), TIME-domain analysis, RADIO telescopes, SPECTRUM analysis, IMAGING systems
Abstract

We report on a time-domain search for pulsars in 44 steep spectrum radio sources originally identified from recent imaging surveys. The time-domain search was conducted at 327 MHz using the Ooty radio telescope, and utilized a semicoherent dedispersion scheme, retaining the sensitivity even for submillisecond periods up to reasonably high dispersion measures. No new pulsars were found. We discuss the nature of these steep spectrum sources and argue that the majority of the sources in our sample should either be pulsars or a new category of galactic sources. Several possibilities that could hinder detection of these sources as pulsars, including anomalously high scattering or alignment of the rotation and magnetic axes, are discussed in detail, and we suggest unconventional search methods to further probe these possibilities. [ABSTRACT FROM AUTHOR]

Published
2018
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65. A LOFAR DETECTION OF THE LOW-MASS YOUNG STAR T TAU AT 149 MHz.

Author

Colm P. Coughlan, Rachael E. Ainsworth, Tom P. Ray, Alexander J. van der Horst, Sera Markoff, Ralph A. M. J. Wijers, Malgorzata Pietka, Adam J. Stewart, Jochen Eislöffel, Matthias Hoeft, Alexander Drabent, Anna M. M. Scaife, Martin E. Bell, Jess W. Broderick, Joeri van Leeuwen, Stéphane Corbel, Philippe Zarka, and Jean-Mathias Grießmeier

Subjects
RADIO observations of artificial satellites, FREQUENCY spectra, LOW mass stars, T Tauri stars, PROTOSTARS, RADIATION
Abstract

Radio observations of young stellar objects (YSOs) enable the study of ionized 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 ionized plasma (local electron density, ionized 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 ( cm−3), ionized gas mass (), and emission measure ( pc cm−6). [ABSTRACT FROM AUTHOR]

Published
2017
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66. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

Author

P. Maat, Benjamin Stappers, Heino Falcke, Charlotte Sobey, Emanuela Orrú, Jason W. T. Hessels, E. Rol, L. Bähren, H. Meulman, Joris P. W. Verbiest, C. Tasse, A. Alexov, Matthias Hoeft, M. A. Garrett, Sarod Yatawatta, James Miller-Jones, Evan Keane, Michael Kramer, S. ter Veen, J. Masters, A. W. Gunst, Casey J. Law, Jochen Eislöffel, B. Scheers, Maaijke Mevius, T. E. Hassall, J. W. Broderick, R. C. Vermeulen, B. Ciardi, Martin Bell, John McKean, Luitje Koopmans, J. E. Noordam, Gerard H. Kuper, Annalisa Bonafede, Harvey Butcher, Sera Markoff, M. P. van Haarlem, E. J. Daw, Rudy Wijnands, M. Kuniyoshi, V. I. Kondratiev, M. Pandey-Pommier, A. Noutsos, K. Zagkouris, Michael R. Bell, H. Paas, J. Sluman, Michiel A. Brentjens, Ashish Asgekar, Roberto Pizzo, Marcus Brüggen, C. G. M. Sterks, W. Reich, R. A. Osten, Albert-Jan Boonstra, Michel Tagger, Stephane Corbel, A. G. Polatidis, P.G. Jonker, M. Gerbers, Stefan J. Wijnholds, J. van Leeuwen, H. Spreeuw, A. de Jong, Matthias Steinmetz, R. J. van Weeren, P. Zarka, K. Lazaridis, George Heald, Mark J. Bentum, G. M. Loose, W. N. Brouw, Patrick Weltevrede, V. S. Dhillon, Aris Karastergiou, Michael W. Wise, Gianni Bernardi, M. Serylak, Rob Fender, Ralph A. M. J. Wijers, H. J. A. Röttgering, H. A. Holties, Y. Tang, Anna M. M. Scaife, Olaf Wucknitz, H. Munk, John D. Swinbank, Jean-Mathias Griessmeier, Vishambhar Pandey, Philip Best, Pim Schellart, T. Coenen, Kenneth C. Anderson, Kapteyn Astronomical Institute, Astronomy, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Netherlands Institute for Radio Astronomy (ASTRON), Max-Planck-Institut für Radioastronomie (MPIFR), Oxford Astrophysics, University of Oxford [Oxford], 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), 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), University of Southampton, Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), 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), University of Sheffield [Sheffield], Thüringer Landessternwarte Tautenburg (TLS), Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud university [Nijmegen], Space Telescope Science Institute (STSci), School of Physics and Astronomy [Southampton], Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, 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), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, University of Edinburgh, Jacobs University [Bremen], Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Leiden Observatory [Leiden], Universiteit Leiden [Leiden], National Radio Astronomy Observatory (NRAO), Applied Stochastics (IMAPP), Centre de Recherche Astrophysique de Lyon (CRAL), 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), Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), Center for Information Technology CIT, Université de Groningen, Netherlands Foundation for Scientific Research. Joeri van Leeuwen and ThijsCoenen are supported by the Netherlands Research School for Astronomy (GrantNOVA3-NW3-2.3.1), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), European Project: 236394,EC:FP7:PEOPLE,FP7-PEOPLE-IEF-2008,PULSAR SURVEY(2010), Hassall, T.E., Stappers, B.W., Hessels, J.W.T., Kramer, M., Alexov, A., Anderson, K., Coenen, T., Karastergiou, A., Keane, E.F., Kondratiev, V.I., Lazaridis, K., Van Leeuwen, J., Noutsos, A., Serylak, M., Sobey, C., Verbiest, J.P.W., Weltevrede, P., Zagkouris, K., Fender, R., Wijers, R.A.M.J., Bähren, L., Bell, M.E., Broderick, J.W., Corbel, S., Daw, E.J., Dhillon, V.S., Eislöffel, J., Falcke, H., Grießmeier, J.-M., Jonker, P., Law, C., Markoff, S., Miller-Jones, J.C.A., Osten, R., Rol, E., Scaife, A.M.M., Scheers, B., Schellart, P., Spreeuw, H., Swinbank, J., Ter Veen, S., Wise, M.W., Wijnands, R., Wucknitz, O., Zarka, P., Asgekar, A., Bell, M.R., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Boonstra, A.J., Brentjens, M., Brouw, W.N., Brüggen, M., Butcher, H.R., Ciardi, B., Garrett, M.A., Gerbers, M., Gunst, A.W., Van Haarlem, M.P., Heald, G., Hoeft, M., Holties, H., De Jong, A., Koopmans, L.V.E., Kuniyoshi, M., Kuper, G., Loose, G.M., Maat, P., Masters, J., McKean, J.P., Meulman, H., Mevius, M., Munk, H., Noordam, J.E., Orrú, E., Paas, H., Pandey-Pommier, M., Pandey, V.N., Pizzo, R., Polatidis, A., Reich, W., Röttgering, H., Sluman, J., Steinmetz, M., Sterks, C.G.M., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., Van Weeren, R.J., Wijnholds, S.J., Yatawatta, S., University of Oxford, 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), Radboud University [Nijmegen], Harvard University-Smithsonian Institution, Universiteit Leiden, 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), 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, 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), Rhodes University, SKA South Africa, and Ska South Africa

Subjects
010504 meteorology & atmospheric sciences, Astronomy, Magnetosphere, Astrophysics, magnetic fields, 01 natural sciences, law.invention, law, Dispersion (optics), 010303 astronomy & astrophysics, Telescope, High Energy Astrophysical Phenomena (astro-ph.HE), Physics, [PHYS]Physics [physics], Astrophysics::Instrumentation and Methods for Astrophysics, SPECTRAL BEHAVIOR, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Astrophysics - High Energy Astrophysical Phenomena, ARRIVAL-TIME DELAY, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, SUPERDISPERSION DELAY, EMPIRICAL-THEORY, Pulsar, pulsars: general, 0103 physical sciences, Astrophysics::Galaxy Astrophysics, 0105 earth and related environmental sciences, ISM: general, METIS-287956, Gravitational wave, Astronomy and Astrophysics, telescopes, LOFAR, Astronomy and Astrophysic, EWI-22107, Pulse (physics), PULSES, Interstellar medium, PSR 0809&74, FREQUENCY-DEPENDENCE, Magnetic field, Space and Planetary Science, [SDU]Sciences of the Universe [physics], RADIO-EMISSION, IR-80985, REFRACTION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], INTERSTELLAR SCATTERING
Abstract

Dispersion in the interstellar medium is a well known phenomenon that follows a simple relationship, which has been used to predict the time delay of dispersed radio pulses since the late 1960s. We performed wide-band simultaneous observations of four pulsars with LOFAR (at 40-190 MHz), the 76-m Lovell Telescope (at 1400 MHz) and the Effelsberg 100-m Telescope (at 8000 MHz) to test the accuracy of the dispersion law over a broad frequency range. In this paper we present the results of these observations which show that the dispersion law is accurate to better than 1 part in 100000 across our observing band. We use this fact to constrain some of the properties of the ISM along the line-of-sight and use the lack of any aberration or retardation effects to determine upper limits on emission heights in the pulsar magnetosphere. We also discuss the effect of pulse profile evolution on our observations, and the implications that it could have for precision pulsar timing projects such as the detection of gravitational waves with pulsar timing arrays., 20 Pages, 14 Figures, Accepted for publication in Astronomy & Astrophysics

Published
2012
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