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1. Wide-Band, Low-Frequency Pulse Profiles of 100 Radio Pulsars with LOFAR

Author: Pilia, M., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Kramer, M., van Leeuwen, J., Weltevrede, P., Lyne, A. G., Zagkouris, K., Hassall, T. E., Bilous, A. V., Breton, R. P., Falcke, H., Grießmeier, J. -M., Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Osłowski, S., Serylak, M., Sobey, C., ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Ciardi, B., Corbel, S., de Geus, E., de Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J. C. A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J. D., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, M. C., van der Horst, A. J., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wijnholds, S. J., Wucknitz, O., and Zarka, P.
Subjects: Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, Astrophysics - Instrumentation and Methods for Astrophysics, Astrophysics - Solar and Stellar Astrophysics
Abstract: LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well-suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects: such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: High Band (120-167 MHz, 100 profiles) and Low Band (15-62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and1400 MHz) in order to study the profile evolution. The profiles are aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. We find that the profile evolution with decreasing radio frequency does not follow a specific trend but, depending on the geometry of the pulsar, new components can enter into, or be hidden from, view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. We offer this catalog of low-frequency pulsar profiles in a user friendly way via the EPN Database of Pulsar Profiles (http://www.epta.eu.org/epndb/)., Comment: 38 pages, 11 figures, 5 tables, A&A in press, updated with editorial corrections
Published: 2015
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2. Pulsar polarisation below 200 MHz: Average profiles and propagation effects

Author: Noutsos, A., Sobey, C., Kondratiev, V. I., Weltevrede, P., Verbiest, J. P. W., Karastergiou, A., Kramer, M., Kuniyoshi, M., Alexov, A., Breton, R. P., Bilous, A. V., Cooper, S., Falcke, H., Grießmeier, J. -M., Hassall, T. E., Hessels, J. W. T., Keane, E. F., Osłowski, S., Pilia, M., Serylak, M., Stappers, B. W., ter Veen, S., van Leeuwen, J., Zagkouris, K., Anderson, K., Bähren, L., Bell, M., Broderick, J., Carbone, D., Cendes, Y., Coenen, T., Corbel, S., Eislöffel, J., Fender, R., Garsden, H., Jonker, P., Law, C., Marko, S., Masters, J., Miller-Jones, J., Molenaar, G., Osten, R., Pietka, M., Rol, E., Rowlinson, A., Scheers, B., Spreeuw, H., Staley, T., Stewart, A., Swinbank, J., Wijers, R., Wijnands, R., Wise, M., Zarka, P., and van der Horst, A.
Subjects: Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract: We present the highest-quality polarisation profiles to date of 16 non-recycled pulsars and four millisecond pulsars, observed below 200 MHz with the LOFAR high-band antennas. Based on the observed profiles, we perform an initial investigation of expected observational effects resulting from the propagation of polarised emission in the pulsar magnetosphere and the interstellar medium. The predictions of magnetospheric birefringence in pulsars have been tested using spectra of the pulse width and fractional polarisation from multifrequency data. The derived spectra offer only partial support for the expected effects of birefringence on the polarisation properties, with only about half of our sample being consistent with the model's predictions. It is noted that for some pulsars these measurements are contaminated by the effects of interstellar scattering. For a number of pulsars in our sample, we have observed significant variations in the amount of Faraday rotation as a function of pulse phase, which is possibly an artefact of scattering. These variations are typically two orders of magnitude smaller than that observed at 1400 MHz by Noutsos et al. (2009), for a different sample of southern pulsars. In this paper we present a possible explanation for the difference in magnitude of this effect between the two frequencies, based on scattering. Finally, we have estimated the magnetospheric emission heights of low-frequency radiation from four pulsars, based on the phase lags between the flux-density and the PA profiles, and the theoretical framework of Blaskiewicz, Cordes & Wasserman (1991). These estimates yielded heights of a few hundred km; at least for PSR B1133+16, this is consistent with emission heights derived based on radius-to-frequency mapping, but is up to a few times larger than the recent upper limit based on pulsar timing., Comment: 27 pages, 11 figures, 2 tables, A&A accepted
Published: 2015
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3. The LOFAR Pilot Surveys for Pulsars and Fast Radio Transients

Author: Coenen, Thijs, van Leeuwen, Joeri, Hessels, Jason W. T., Stappers, Ben W., Kondratiev, Vladislav I., Alexov, A., Breton, R. P., Bilous, A., Cooper, S., Falcke, H., Fallows, R. A., Gajjar, V., Grießmeier, J. -M., Hassall, T. E., Karastergiou, A., Keane, E. F., Kramer, M., Kuniyoshi, M., Noutsos, A., Osłowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, C., ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., van Amesfoort, A. S., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H. R., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., de Gasperin, F., de Geus, E., Gunst, A. W., Hamaker, J. P., Heald, G., Hoeft, M., van der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J. P., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A. G., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A. M. M., Schwarz, D., Sluman, J., Smirnov, O., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, C., Vermeulen, R., Vocks, C., van Weeren, R. J., Wucknitz, O., Zarka, P., and Zensus, A.
Subjects: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times. Each observation covered ~75 sq. deg using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 sq. deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 /day/sky, for bursts brighter than S > 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array., Comment: 18 pages, 10 figures, accepted for A&A
Published: 2014
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4. Differential Frequency-dependent Delay from the Pulsar Magnetosphere

Author: Hassall, T. E., Stappers, B. W., Weltevrede, P., Hessels, J. W. T., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E. F., Kondratiev, V. I., van Leeuwen, J., Noutsos, A., Pilia, M., Serylak, M., Sobey, C., Zagkouris, K., Fender, R., Bell, M. E., Broderick, J., Eisloffel, J., Falcke, H., Griessmeier, J. -M., Kuniyoshi, M., Miller-Jones, J. C. A., Wise, M. W., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M. J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Bruggen, M., Butcher, H. R., Ciardi, B., de Gasperin, F., de Reijer, J. -P., Duscha, S., Fallows, R. A., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J. P., Norden, M. J., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Rottgering, H., Sluman, J., Tang, Y., Tasse, C., Vermeulen, R., van Weeren, R. J., Wijnholds, S. J., and Yatawatta, S.
Subjects: Astrophysics - Solar and Stellar Astrophysics, Astrophysics - High Energy Astrophysical Phenomena
Abstract: Some radio pulsars show clear drifting subpulses, in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14-5100 MHz. Despite this, the shapes of the driftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies (< 500 MHz), a discrete step of 180 degrees in subpulse phase is observed at higher frequencies (> 820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency - one driftband arriving 30 pulses earlier at 20 MHz than it does at 1380 MHz, whilst the other arrives simultaneously at all frequencies. The drifting pattern which is observed here cannot be explained by either the rotating carousel model or the surface oscillation model, and could provide new insight into the physical processes happening within the pulsar magnetosphere., Comment: 10 pages, 6 figures, accepted for publication in Astronomy and Astrophysics
Published: 2013
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5. Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations

Author: 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., Bahren, L., Bell, M. E., Broderick, J. W., Corbel, S., Daw, E. J., Dhillon, V. S., Eisloffel, 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., Bruggen, 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., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V. N., Pizzo, R., Polatidis, A., Reich, W., Rottgering, H., Sluman, J., Steinmetz, M., Sterks, C. G. M., Tagger, M., Tang, Y., Tasse, C., Vermeulen, R., van Weeren, R. J., Wijnholds, S. J., and Yatawatta, S.
Subjects: Astrophysics - High Energy Astrophysical Phenomena
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., Comment: 20 Pages, 14 Figures, Accepted for publication in Astronomy & Astrophysics
Published: 2012
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6. A GPU-based survey for millisecond radio transients using ARTEMIS

Author: Armour, W., Karastergiou, A., Giles, M., Williams, C., Magro, A., Zagkouris, K., Roberts, S., Salvini, S., Dulwich, F., and Mort, B.
Subjects: Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: Astrophysical radio transients are excellent probes of extreme physical processes originating from compact sources within our Galaxy and beyond. Radio frequency signals emitted from these objects provide a means to study the intervening medium through which they travel. Next generation radio telescopes are designed to explore the vast unexplored parameter space of high time resolution astronomy, but require High Performance Computing (HPC) solutions to process the enormous volumes of data that are produced by these telescopes. We have developed a combined software /hardware solution (code named ARTEMIS) for real-time searches for millisecond radio transients, which uses GPU technology to remove interstellar dispersion and detect millisecond radio bursts from astronomical sources in real-time. Here we present an introduction to ARTEMIS. We give a brief overview of the software pipeline, then focus specifically on the intricacies of performing incoherent de-dispersion. We present results from two brute-force algorithms. The first is a GPU based algorithm, designed to exploit the L1 cache of the NVIDIA Fermi GPU. Our second algorithm is CPU based and exploits the new AVX units in Intel Sandy Bridge CPUs., Comment: 4 pages, 7 figures. To appear in the proceedings of ADASS XXI, ed. P.Ballester and D.Egret, ASP Conf. Ser
Published: 2011

7. Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

Author: 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., Veen, S. ter, Vermeulen, R., van de Brink, R. H., van Weeren, R. J., Wijers, R. A. M. J., Wise, M. W., Wucknitz, O., Yatawatta, S., and Zarka, P.
Published: 2013
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8. Scattering analysis of LOFAR pulsar observations

Author: Geyer, M., primary, Karastergiou, A., additional, Kondratiev, V. I., additional, Zagkouris, K., additional, Kramer, M., additional, Stappers, B. W., additional, Grießmeier, J.-M., additional, Hessels, J. W. T., additional, Michilli, D., additional, Pilia, M., additional, and Sobey, C., additional
Published: 2017
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9. Scattering analysis of LOFAR pulsar observations

Author: Geyer, M., Karastergiou, A., Kondratiev, V., Zagkouris, K., Kramer, M., Stappers, B., Grießmeier, J., Hessels, J., Michilli, D., Pilia, M., Sobey, Charlotte, Geyer, M., Karastergiou, A., Kondratiev, V., Zagkouris, K., Kramer, M., Stappers, B., Grießmeier, J., Hessels, J., Michilli, D., Pilia, M., and Sobey, Charlotte
Abstract: © 2017 The Authors Published by Oxford University Press. We measure the effects of interstellar scattering on average pulse profiles from 13 radio pulsars with simple pulse shapes. We use data from the LOFAR High Band Antennas, at frequencies between 110 and 190 MHz.We apply a forward fitting technique, and simultaneously determine the intrinsic pulse shape, assuming single Gaussian component profiles. We find that the constant t , associated with scattering by a single thin screen, has a power-law dependence on frequency t ? ? -a , with indices ranging from a = 1.50 to 4.0, despite simplest theoretical models predicting a =4.0 or 4.4. Modelling the screen as an isotropic or extremely anisotropic scatterer, we find anisotropic scattering fits lead to larger power-law indices, often in better agreement with theoretically expected values.We compare the scattering models based on the inferred, frequency-dependent parameters of the intrinsic pulse, and the resulting correction to the dispersion measure (DM). We highlight the cases in which fits of extreme anisotropic scattering are appealing, while stressing that the data do not strictly favour either model for any of the 13 pulsars. The pulsars show anomalous scattering properties that are consistent with finite scattering screens and/or anisotropy, but these data alone do not provide the means for an unambiguous characterization of the screens. We revisit the empirical t versus DM relation and consider how our results support a frequency dependence of a. Very long baseline interferometry, and observations of the scattering and scintillation properties of these sources at higher frequencies, will provide further evidence.
Published: 2017

10. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

Author: Pilia, M., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Kramer, M., van Leeuwen, J., Weltevrede, P., Lyne, A. G., Zagkouris, K., Hassall, T. E., Bilous, A. V., Breton, R. P., Falcke, H., Grießmeier, J. -M, Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Serylak, M., Sobey, C., ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Ciardi, B., Corbel, S., de Geus, E., de Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J. C. A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J. D., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., van der Horst, A. J., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wijnholds, S. J., Wucknitz, O., Zarka, P., Pilia, M., Hessels, J. W. T., Stappers, B. W., Kondratiev, V. I., Kramer, M., van Leeuwen, J., Weltevrede, P., Lyne, A. G., Zagkouris, K., Hassall, T. E., Bilous, A. V., Breton, R. P., Falcke, H., Grießmeier, J. -M, Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Os\lowski, S., Serylak, M., Sobey, C., ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I. M., Bell, M. E., Bentum, M. J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J. W., Brüggen, M., Ciardi, B., Corbel, S., de Geus, E., de Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R. A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Hamaker, J. P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J. C. A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A. G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J. D., Tagger, M., Tang, Y., Tasse, C., Thoudam, Satyendra, Toribio, M. C., van der Horst, A. J., Vermeulen, R., Vocks, C., van Weeren, R. J., Wijers, R. A. M. J., Wijnands, R., Wijnholds, S. J., Wucknitz, O., and Zarka, P.
Abstract: Context. LOFAR offers the unique capability of observing pulsars across the 10−240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. Aims. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. Methods. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: high band (120–167 MHz, 100 profiles) and low band (15–62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and 1400 MHz) to study the profile evolution. The profiles were aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. Results. We find that the profile evolution with decreasing radio frequency does not follow a specific trend; depending on the geometry of the pulsar, new components can enter into or be hidden from view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories.
Published: 2016
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11. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

Author: Pilia, M., primary, Hessels, J. W. T., additional, Stappers, B. W., additional, Kondratiev, V. I., additional, Kramer, M., additional, van Leeuwen, J., additional, Weltevrede, P., additional, Lyne, A. G., additional, Zagkouris, K., additional, Hassall, T. E., additional, Bilous, A. V., additional, Breton, R. P., additional, Falcke, H., additional, Grießmeier, J.-M., additional, Keane, E., additional, Karastergiou, A., additional, Kuniyoshi, M., additional, Noutsos, A., additional, Osłowski, S., additional, Serylak, M., additional, Sobey, C., additional, ter Veen, S., additional, Alexov, A., additional, Anderson, J., additional, Asgekar, A., additional, Avruch, I. M., additional, Bell, M. E., additional, Bentum, M. J., additional, Bernardi, G., additional, Bîrzan, L., additional, Bonafede, A., additional, Breitling, F., additional, Broderick, J. W., additional, Brüggen, M., additional, Ciardi, B., additional, Corbel, S., additional, de Geus, E., additional, de Jong, A., additional, Deller, A., additional, Duscha, S., additional, Eislöffel, J., additional, Fallows, R. A., additional, Fender, R., additional, Ferrari, C., additional, Frieswijk, W., additional, Garrett, M. A., additional, Gunst, A. W., additional, Hamaker, J. P., additional, Heald, G., additional, Horneffer, A., additional, Jonker, P., additional, Juette, E., additional, Kuper, G., additional, Maat, P., additional, Mann, G., additional, Markoff, S., additional, McFadden, R., additional, McKay-Bukowski, D., additional, Miller-Jones, J. C. A., additional, Nelles, A., additional, Paas, H., additional, Pandey-Pommier, M., additional, Pietka, M., additional, Pizzo, R., additional, Polatidis, A. G., additional, Reich, W., additional, Röttgering, H., additional, Rowlinson, A., additional, Schwarz, D., additional, Smirnov, O., additional, Steinmetz, M., additional, Stewart, A., additional, Swinbank, J. D., additional, Tagger, M., additional, Tang, Y., additional, Tasse, C., additional, Thoudam, S., additional, Toribio, M. C., additional, van der Horst, A. J., additional, Vermeulen, R., additional, Vocks, C., additional, van Weeren, R. J., additional, Wijers, R. A. M. J., additional, Wijnands, R., additional, Wijnholds, S. J., additional, Wucknitz, O., additional, and Zarka, P., additional
Published: 2016
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12. Pulsar polarisation below 200 MHz: Average profiles and propagation effects

Author: Noutsos, A., primary, Sobey, C., additional, Kondratiev, V. I., additional, Weltevrede, P., additional, Verbiest, J. P. W., additional, Karastergiou, A., additional, Kramer, M., additional, Kuniyoshi, M., additional, Alexov, A., additional, Breton, R. P., additional, Bilous, A. V., additional, Cooper, S., additional, Falcke, H., additional, Grießmeier, J.-M., additional, Hassall, T. E., additional, Hessels, J. W. T., additional, Keane, E. F., additional, Osłowski, S., additional, Pilia, M., additional, Serylak, M., additional, Stappers, B. W., additional, ter Veen, S., additional, van Leeuwen, J., additional, Zagkouris, K., additional, Anderson, K., additional, Bähren, L., additional, Bell, M., additional, Broderick, J., additional, Carbone, D., additional, Cendes, Y., additional, Coenen, T., additional, Corbel, S., additional, Eislöffel, J., additional, Fender, R., additional, Garsden, H., additional, Jonker, P., additional, Law, C., additional, Markoff, S., additional, Masters, J., additional, Miller-Jones, J., additional, Molenaar, G., additional, Osten, R., additional, Pietka, M., additional, Rol, E., additional, Rowlinson, A., additional, Scheers, B., additional, Spreeuw, H., additional, Staley, T., additional, Stewart, A., additional, Swinbank, J., additional, Wijers, R., additional, Wijnands, R., additional, Wise, M., additional, Zarka, P., additional, and van der Horst, A., additional
Published: 2015
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13. The LOFAR pilot surveys for pulsars and fast radio transients

Author: Coenen, T., Van Leeuwen, J., Hessels, J., Stappers, B., Kondratiev, V., Alexov, A., Breton, R., Bilous, A., Cooper, S., Falcke, H., Fallows, R., Gajjar, V., Grießmeier, J., Hassall, T., Karastergiou, A., Keane, E., Kramer, M., Kuniyoshi, M., Noutsos, A., Oslowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, Charlotte, Ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., Van Amesfoort, A., Anderson, J., Asgekar, A., Avruch, I., Bell, M., Bentum, M., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M., De Gasperin, F., De Geus, E., Gunst, A., Hamaker, J., Heald, G., Hoeft, M., Van Der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A., Schwarz, D., Sluman, J., Smirnov, O., Swinbank, J., Coenen, T., Van Leeuwen, J., Hessels, J., Stappers, B., Kondratiev, V., Alexov, A., Breton, R., Bilous, A., Cooper, S., Falcke, H., Fallows, R., Gajjar, V., Grießmeier, J., Hassall, T., Karastergiou, A., Keane, E., Kramer, M., Kuniyoshi, M., Noutsos, A., Oslowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, Charlotte, Ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., Van Amesfoort, A., Anderson, J., Asgekar, A., Avruch, I., Bell, M., Bentum, M., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M., De Gasperin, F., De Geus, E., Gunst, A., Hamaker, J., Heald, G., Hoeft, M., Van Der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A., Schwarz, D., Sluman, J., Smirnov, O., and Swinbank, J.
Abstract: © 2014 ESO .We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~ 1.4 × 104 deg2, with 1 h dwell times. Each observation covered ~75 deg2 using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 deg2, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 deg2 per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 day-1 sky-1, for bursts brighter than S> 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array.
Published: 2014

14. The LOFAR pilot surveys for pulsars and fast radio transients

Author: Coenen, Thijs, primary, van Leeuwen, Joeri, additional, Hessels, Jason W. T., additional, Stappers, Ben W., additional, Kondratiev, Vladislav I., additional, Alexov, A., additional, Breton, R. P., additional, Bilous, A., additional, Cooper, S., additional, Falcke, H., additional, Fallows, R. A., additional, Gajjar, V., additional, Grießmeier, J.-M., additional, Hassall, T. E., additional, Karastergiou, A., additional, Keane, E. F., additional, Kramer, M., additional, Kuniyoshi, M., additional, Noutsos, A., additional, Osłowski, S., additional, Pilia, M., additional, Serylak, M., additional, Schrijvers, C., additional, Sobey, C., additional, ter Veen, S., additional, Verbiest, J., additional, Weltevrede, P., additional, Wijnholds, S., additional, Zagkouris, K., additional, van Amesfoort, A. S., additional, Anderson, J., additional, Asgekar, A., additional, Avruch, I. M., additional, Bell, M. E., additional, Bentum, M. J., additional, Bernardi, G., additional, Best, P., additional, Bonafede, A., additional, Breitling, F., additional, Broderick, J., additional, Brüggen, M., additional, Butcher, H. R., additional, Ciardi, B., additional, Corstanje, A., additional, Deller, A., additional, Duscha, S., additional, Eislöffel, J., additional, Fender, R., additional, Ferrari, C., additional, Frieswijk, W., additional, Garrett, M. A., additional, de Gasperin, F., additional, de Geus, E., additional, Gunst, A. W., additional, Hamaker, J. P., additional, Heald, G., additional, Hoeft, M., additional, van der Horst, A., additional, Juette, E., additional, Kuper, G., additional, Law, C., additional, Mann, G., additional, McFadden, R., additional, McKay-Bukowski, D., additional, McKean, J. P., additional, Munk, H., additional, Orru, E., additional, Paas, H., additional, Pandey-Pommier, M., additional, Polatidis, A. G., additional, Reich, W., additional, Renting, A., additional, Röttgering, H., additional, Rowlinson, A., additional, Scaife, A. M. M., additional, Schwarz, D., additional, Sluman, J., additional, Smirnov, O., additional, Swinbank, J., additional, Tagger, M., additional, Tang, Y., additional, Tasse, C., additional, Thoudam, S., additional, Toribio, C., additional, Vermeulen, R., additional, Vocks, C., additional, van Weeren, R. J., additional, Wucknitz, O., additional, Zarka, P., additional, and Zensus, A., additional
Published: 2014
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15. Differential frequency-dependent delay from the pulsar magnetosphere

Author: Hassall, T.E., Stappers, B.W., Weltevrede, P., Hessels, W.T., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E.F., Kondratiev, V.I., Leeuwen, J. van, Noutsos, A., Pilia, M., Serylak, M, Sobey, C, Zagkouris, K., Fender, R., Bell, M.E., Broderick, J., Eislöffel, J., Falcke, H., Griessmeier, J.M., Kuniyoshi, M., Miller-Jones, J.C.A., Wise, M.W., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brüggen, M., Butcher, H.R., Wijnholds, S.J., Yatawatta, S., Hassall, T.E., Stappers, B.W., Weltevrede, P., Hessels, W.T., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E.F., Kondratiev, V.I., Leeuwen, J. van, Noutsos, A., Pilia, M., Serylak, M, Sobey, C, Zagkouris, K., Fender, R., Bell, M.E., Broderick, J., Eislöffel, J., Falcke, H., Griessmeier, J.M., Kuniyoshi, M., Miller-Jones, J.C.A., Wise, M.W., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brüggen, M., Butcher, H.R., Wijnholds, S.J., and Yatawatta, S.
Abstract: Contains fulltext : 111321.pdf (preprint version ) (Open Access)
Published: 2013

16. Differential frequency-dependent delay from the pulsar magnetosphere

Author: Hassall, T. E, Stappers, B. W., Weltevrede, P, Hessels, J. W. T., Alexov, A, Coenen, T, Karastergiou, A, Kramer, M, Keane, E. F., Kondratiev, V. I., van Leeuwen, J, Noutsos, A, Pilia, M, Serylak, M, Sobey, C, Zagkouris, K, Fender, R, Bell, M. E., Broderick, J, Eislo-el, J, Falcke, H, Griebmeier, J M, Kuniyoshi, M, Miller-Jones, J. C. A., Wise, M J, Wucknitz, O, Zarka, P, Asgekar, A, Batejat, F, Bentum, M J, Bernardi, G, Best, Phillip, Bonafede, A, Breitling, F, Bruggen, M, Butcher, Harvey, Ciardi, Benedetta, de Gasperin, F, de Reijer, J.-P., Duscha, S., Fallows, R. A., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J. P., Norden, M. J., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Rottgering, Hubb, Sluman, J., Tang, T., Tasse, C., Vermeulen, R. C., van Weeren, R. J., Wijnholds, S. J., Yatawatta, S., Tang, Y, Hassall, T. E, Stappers, B. W., Weltevrede, P, Hessels, J. W. T., Alexov, A, Coenen, T, Karastergiou, A, Kramer, M, Keane, E. F., Kondratiev, V. I., van Leeuwen, J, Noutsos, A, Pilia, M, Serylak, M, Sobey, C, Zagkouris, K, Fender, R, Bell, M. E., Broderick, J, Eislo-el, J, Falcke, H, Griebmeier, J M, Kuniyoshi, M, Miller-Jones, J. C. A., Wise, M J, Wucknitz, O, Zarka, P, Asgekar, A, Batejat, F, Bentum, M J, Bernardi, G, Best, Phillip, Bonafede, A, Breitling, F, Bruggen, M, Butcher, Harvey, Ciardi, Benedetta, de Gasperin, F, de Reijer, J.-P., Duscha, S., Fallows, R. A., Ferrari, C., Frieswijk, W., Garrett, M. A., Gunst, A. W., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J. P., Norden, M. J., Pandey-Pommier, M., Pizzo, R., Polatidis, A. G., Reich, W., Rottgering, Hubb, Sluman, J., Tang, T., Tasse, C., Vermeulen, R. C., van Weeren, R. J., Wijnholds, S. J., Yatawatta, S., and Tang, Y
Abstract: Some radio pulsars show clear "drifting subpulses", in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subp
Published: 2013

17. Differential frequency-dependent delay from the pulsar magnetosphere

Author: Hassall, T., Stappers, B., Weltevrede, P., Hessels, J., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E., Kondratiev, V., van Leeuwen, J., Noutsos, A., Pilia, M., Serylak, M., Sobey, C., Zagkouris, K., Fender, R., Bell, M., Broderick, J., Eisloeffel, J., Falcke, H., Griessmeier, J., Kuniyoshi, M., Miller-Jones, James, Wise, M., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M., BERNARDI, G., Best, P., Bonafede, A., Breitling, F., Brueggen, M., Butcher, H., Ciardi, B., de Gasperin, F., de Reijer, J., Duscha, S., Fallows, R., Ferrari, C., Frieswijk, W., Garrett, M., Gunst, A., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J., Norden, M., Pandey-Pommier, M., Pizzo, R., Polatidis, A., Reich, W., Roettgering, H., Sluman, J., Tang, Y., Tasse, C., Vermeulen, R., van Weeren, R., Wijnholds, S., Yatawatta, S., Hassall, T., Stappers, B., Weltevrede, P., Hessels, J., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E., Kondratiev, V., van Leeuwen, J., Noutsos, A., Pilia, M., Serylak, M., Sobey, C., Zagkouris, K., Fender, R., Bell, M., Broderick, J., Eisloeffel, J., Falcke, H., Griessmeier, J., Kuniyoshi, M., Miller-Jones, James, Wise, M., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M., BERNARDI, G., Best, P., Bonafede, A., Breitling, F., Brueggen, M., Butcher, H., Ciardi, B., de Gasperin, F., de Reijer, J., Duscha, S., Fallows, R., Ferrari, C., Frieswijk, W., Garrett, M., Gunst, A., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J., Norden, M., Pandey-Pommier, M., Pizzo, R., Polatidis, A., Reich, W., Roettgering, H., Sluman, J., Tang, Y., Tasse, C., Vermeulen, R., van Weeren, R., Wijnholds, S., and Yatawatta, S.
Abstract: Some radio pulsars show clear "drifting subpulses", in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14-5100 MHz. Despite this, the shapes of the driftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies (<500 MHz), a discrete step of ~180° in subpulse phase is observed at higher frequencies (>820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency - one driftband arriving 30 pulses earlier at 20 MHz than it does at 1380 MHz, whilst the other arrives simultaneously at all frequencies. The drifting pattern which is observed here cannot be explained by either the rotating carousel model or the surface oscillation model, and could provide new insight into the physical processes happening within the pulsar magnetosphere.
Published: 2013

18. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

Author: Hassall, T., Stappers, B., Hessels, J., Kramer, M., Alexov, A., Anderson, K., Coenen, T., Karastergiou, A., Keane, E., Kondratiev, V., Lazaridis, K., van Leeuwen, J., Noutsos, A., Serylak, M., Sobey, C., Verbiest, J., Weltevrede, P., Zagkouris, K., Fender, R., Wijers, R., Baehren, L., Bell, M., Broderick, J., Corbel, S., Daw, E., Dhillon, V., Eisloeffel, J., Falcke, H., Griessmeier, J., Jonker, P., Law, C., Markoff, S., Miller-Jones, James, Osten, R., Rol, E., Scaife, A., Scheers, B., Schellart, P., Spreeuw, H., Swinbank, J., ter Veen, S., Wise, M., Wijnands, R., Wucknitz, O., Zarka, P., Asgekar, A., Bentum, M., BERNARDI, G., Best, P., Bonafede, A., Boonstra, A., Brentjens, M., Brouw, W., Brueggen, M., Butcher, H., Ciardi, B., Garrett, M., Gerbers, M., Gunst, A., van Haarlem, M., Heald, G., Hoeft, M., Holties, H., de Jong, A., Koopmans, L., Kuniyoshi, M., Kuper, G., Loose, G., Maat, P., Masters, J., McKean, J., Meulman, H., Mevius, M., Munk, H., Noordam, J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V., Pizzo, R., Polatidis, A., Reich, W., Rottgering, H., Sluman, J., Steinmetz, M., Sterks, C., Tagger, M., Yang, T., Tasse, C., Vermeulen, R., van Weeren, R., Wijnholds, S., Yatawatta, S., Hassall, T., Stappers, B., Hessels, J., Kramer, M., Alexov, A., Anderson, K., Coenen, T., Karastergiou, A., Keane, E., Kondratiev, V., Lazaridis, K., van Leeuwen, J., Noutsos, A., Serylak, M., Sobey, C., Verbiest, J., Weltevrede, P., Zagkouris, K., Fender, R., Wijers, R., Baehren, L., Bell, M., Broderick, J., Corbel, S., Daw, E., Dhillon, V., Eisloeffel, J., Falcke, H., Griessmeier, J., Jonker, P., Law, C., Markoff, S., Miller-Jones, James, Osten, R., Rol, E., Scaife, A., Scheers, B., Schellart, P., Spreeuw, H., Swinbank, J., ter Veen, S., Wise, M., Wijnands, R., Wucknitz, O., Zarka, P., Asgekar, A., Bentum, M., BERNARDI, G., Best, P., Bonafede, A., Boonstra, A., Brentjens, M., Brouw, W., Brueggen, M., Butcher, H., Ciardi, B., Garrett, M., Gerbers, M., Gunst, A., van Haarlem, M., Heald, G., Hoeft, M., Holties, H., de Jong, A., Koopmans, L., Kuniyoshi, M., Kuper, G., Loose, G., Maat, P., Masters, J., McKean, J., Meulman, H., Mevius, M., Munk, H., Noordam, J., Orru, E., Paas, H., Pandey-Pommier, M., Pandey, V., Pizzo, R., Polatidis, A., Reich, W., Rottgering, H., Sluman, J., Steinmetz, M., Sterks, C., Tagger, M., Yang, T., Tasse, C., Vermeulen, R., van Weeren, R., Wijnholds, S., and Yatawatta, S.
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 10^5 across our observing band. We use this fact to constrain some of the properties of the interstellar medium 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.
Published: 2012

19. Differential frequency-dependent delay from the pulsar magnetosphere

Author: Hassall, T. E., primary, Stappers, B. W., additional, Weltevrede, P., additional, Hessels, J. W. T., additional, Alexov, A., additional, Coenen, T., additional, Karastergiou, A., additional, Kramer, M., additional, Keane, E. F., additional, Kondratiev, V. I., additional, van Leeuwen, J., additional, Noutsos, A., additional, Pilia, M., additional, Serylak, M., additional, Sobey, C., additional, Zagkouris, K., additional, Fender, R., additional, Bell, M. E., additional, Broderick, J., additional, Eislöffel, J., additional, Falcke, H., additional, Grießmeier, J.-M., additional, Kuniyoshi, M., additional, Miller-Jones, J. C. A., additional, Wise, M. W., additional, Wucknitz, O., additional, Zarka, P., additional, Asgekar, A., additional, Batejat, F., additional, Bentum, M. J., additional, Bernardi, G., additional, Best, P., additional, Bonafede, A., additional, Breitling, F., additional, Brüggen, M., additional, Butcher, H. R., additional, Ciardi, B., additional, de Gasperin, F., additional, de Reijer, J.-P., additional, Duscha, S., additional, Fallows, R. A., additional, Ferrari, C., additional, Frieswijk, W., additional, Garrett, M. A., additional, Gunst, A. W., additional, Heald, G., additional, Hoeft, M., additional, Juette, E., additional, Maat, P., additional, McKean, J. P., additional, Norden, M. J., additional, Pandey-Pommier, M., additional, Pizzo, R., additional, Polatidis, A. G., additional, Reich, W., additional, Röttgering, H., additional, Sluman, J., additional, Tang, Y., additional, Tasse, C., additional, Vermeulen, R., additional, van Weeren, R. J., additional, Wijnholds, S. J., additional, and Yatawatta, S., additional
Published: 2013
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20. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

Author: Hassall, T. E., primary, Stappers, B. W., additional, Hessels, J. W. T., additional, Kramer, M., additional, Alexov, A., additional, Anderson, K., additional, Coenen, T., additional, Karastergiou, A., additional, Keane, E. F., additional, Kondratiev, V. I., additional, Lazaridis, K., additional, van Leeuwen, J., additional, Noutsos, A., additional, Serylak, M., additional, Sobey, C., additional, Verbiest, J. P. W., additional, Weltevrede, P., additional, Zagkouris, K., additional, Fender, R., additional, Wijers, R. A. M. J., additional, Bähren, L., additional, Bell, M. E., additional, Broderick, J. W., additional, Corbel, S., additional, Daw, E. J., additional, Dhillon, V. S., additional, Eislöffel, J., additional, Falcke, H., additional, Grießmeier, J.-M., additional, Jonker, P., additional, Law, C., additional, Markoff, S., additional, Miller-Jones, J. C. A., additional, Osten, R., additional, Rol, E., additional, Scaife, A. M. M., additional, Scheers, B., additional, Schellart, P., additional, Spreeuw, H., additional, Swinbank, J., additional, ter Veen, S., additional, Wise, M. W., additional, Wijnands, R., additional, Wucknitz, O., additional, Zarka, P., additional, Asgekar, A., additional, Bell, M. R., additional, Bentum, M. J., additional, Bernardi, G., additional, Best, P., additional, Bonafede, A., additional, Boonstra, A. J., additional, Brentjens, M., additional, Brouw, W. N., additional, Brüggen, M., additional, Butcher, H. R., additional, Ciardi, B., additional, Garrett, M. A., additional, Gerbers, M., additional, Gunst, A. W., additional, van Haarlem, M. P., additional, Heald, G., additional, Hoeft, M., additional, Holties, H., additional, de Jong, A., additional, Koopmans, L. V. E., additional, Kuniyoshi, M., additional, Kuper, G., additional, Loose, G. M., additional, Maat, P., additional, Masters, J., additional, McKean, J. P., additional, Meulman, H., additional, Mevius, M., additional, Munk, H., additional, Noordam, J. E., additional, Orrú, E., additional, Paas, H., additional, Pandey-Pommier, M., additional, Pandey, V. N., additional, Pizzo, R., additional, Polatidis, A., additional, Reich, W., additional, Röttgering, H., additional, Sluman, J., additional, Steinmetz, M., additional, Sterks, C. G. M., additional, Tagger, M., additional, Tang, Y., additional, Tasse, C., additional, Vermeulen, R., additional, van Weeren, R. J., additional, Wijnholds, S. J., additional, and Yatawatta, S., additional
Published: 2012
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21. 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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22. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

Author: J. van Leeuwen, Matthias Steinmetz, T. E. Hassall, A. Nelles, E. de Geus, M. Pilia, B. W. Stappers, Heino Falcke, H. J. A. Röttgering, Annalisa Bonafede, Oleg Smirnov, Anna V. Bilous, Satyendra Thoudam, Evan Keane, Peter G. Jonker, W. Frieswijk, Rudy Wijnands, A. Noutsos, M. Pietka, John D. Swinbank, Richard Fallows, R. J. van Weeren, M. Pandey-Pommier, Olaf Wucknitz, A. Alexov, Rebecca McFadden, E. Juette, F. Breitling, Stefan J. Wijnholds, Aris Karastergiou, Benedetta Ciardi, H. Paas, Antonia Rowlinson, Dominik J. Schwarz, Michael Kramer, A. I. F. Stewart, Y. Tang, Ashish Asgekar, K. Zagkouris, James A. Anderson, Chiara Ferrari, S. Duscha, James Miller-Jones, Andrew Lyne, Stefan Oslowski, Adam T. Deller, A. de Jong, R. C. Vermeulen, Gianni Bernardi, I. M. Avruch, M. A. Garrett, M. C. Toribio, Jochen Eislöffel, Charlotte Sobey, A. J. van der Horst, Rene P. Breton, Cyril Tasse, Marcus Brüggen, J. W. Broderick, Gerard H. Kuper, S. ter Veen, A. W. Gunst, Rob Fender, P. Zarka, D. McKay-Bukowski, Martin Bell, A. Horneffer, M. Kuniyoshi, Patrick Weltevrede, M. Serylak, A. G. Polatidis, Ralph A. M. J. Wijers, Mark J. Bentum, Christian Vocks, Jean-Mathias Grießmeier, Sera Markoff, Jason W. T. Hessels, Stephane Corbel, Laura Birzan, J. P. Hamaker, Wolfgang Reich, Michel Tagger, P. Maat, V. I. Kondratiev, George Heald, Gottfried Mann, R. Pizzo, Astronomy, Netherlands Institute for Radio Astronomy (ASTRON), Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], Vrije Universiteit Medical Centre (VUMC), Vrije Universiteit Amsterdam [Amsterdam] (VU), Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Amsterdam [Amsterdam] (UvA), Oxford Astrophysics, University of Oxford, School of Physics and Astronomy [Southampton], University of Southampton, 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), Centre for Astrophysics and Supercomputing [Swinburne] (CAS), Swinburne University of Technology [Melbourne], Department of Physics [Oxford], Max-Planck-Institut für Radioastronomie (MPIFR), Universität Bielefeld = Bielefeld University, University of Cape Town, Space Telescope Science Institute (STSci), Epidémiologie et Biostatistique [Bordeaux], Université Bordeaux Segalen - Bordeaux 2-Institut de Santé Publique, d'Épidémiologie et de Développement (ISPED)-Institut National de la Santé et de la Recherche Médicale (INSERM), SRON Netherlands Institute for Space Research (SRON), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University [Cambridge]-Smithsonian Institution, Leiden Observatory [Leiden], Universiteit Leiden [Leiden], University of Hamburg, Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH / Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures (DSMZ), University of Edinburgh, Max-Planck-Institut für Astrophysik (MPA), Max-Planck-Gesellschaft, 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), Structural Dynamics and Acoustics, University of Twente, Thüringer Landessternwarte Tautenburg (TLS), Institute of Mathematical and Physical Sciences, Department of Astrophysics [Oxford], Département de Géologie, Université de Montréal (UdeM), Astronomisches Institut der Ruhr-Universität Bochum, Ruhr-Universität Bochum [Bochum], Leibniz-Institut für Astrophysik Potsdam (AIP), Department of Physical Sciences, University of Oulu, University of Oulu, Curtin University [Perth], Planning and Transport Research Centre (PATREC), University of Groningen [Groningen], 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-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Australia Telescope National Facility (ATNF), Commonwealth Scientific and Industrial Research Organisation [Canberra] (CSIRO), Institute of Farm Animal Genetics (ING), Friedrich-Loeffler-Institut (FLI), SKA South Africa, Ska South Africa, Astrophysikalisches Institut Potsdam (AIP), Department of Physics [Dunedin], University of Otago [Dunedin, Nouvelle-Zélande], Princeton University, Edinburgh Research Station, Centre for Ecology and Hydrology, 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), Department of Astrophysics [Nijmegen], Radboud University [Nijmegen]-Radboud University [Nijmegen], Anton Pannekoek Institute for Astronomy, Argelander-Institut für Astronomie (AlfA), Rheinische Friedrich-Wilhelms-Universität Bonn, Alexander von Humboldt Foundation Agence Nationale de la Recherche ANR-09-JCJC-0001-01, ANR-09-JCJC-0001,OPALES(2009), European Project: 337062,EC:FP7:ERC,ERC-2013-StG,DRAGNET(2014), European Project: 617199,EC:FP7:ERC,ERC-2013-CoG,ALERT(2014), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), ROUCHON, Nathalie, Jeunes chercheuses et jeunes chercheurs - - OPALES2009 - ANR-09-JCJC-0001 - JCJC - VALID, DRAGNET: A high-speed, wide-angle camera for catching extreme astrophysical events - DRAGNET - - EC:FP7:ERC2014-01-01 - 2018-12-31 - 337062 - VALID, ALERT - The Apertif-LOFAR Exploration of the Radio Transient Sky - ALERT - - EC:FP7:ERC2014-12-01 - 2019-11-30 - 617199 - VALID, Radio pulsars with LOFAR: a study of extreme physics laboratories. - PULSARS WITH LOFAR - - EC:FP7:PEOPLE2008-05-01 - 2012-04-30 - 224838 - VALID, High Energy Astrophys. & Astropart. Phys (API, FNWI), University of Oxford [Oxford], Radboud university [Nijmegen], 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), Fakultät für Physik, Universität Bielefeld, Universität Bielefeld, University of the Western Cape, Cape Town, 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 Twente [Netherlands], Université de Lyon-Université de Lyon-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS), Radboud university [Nijmegen]-Radboud university [Nijmegen], Harvard University-Smithsonian Institution, Universiteit Leiden, École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), Pilia, M., Hessels, J.W.T., Stappers, B.W., Kondratiev, V.I., Kramer, M., Van Leeuwen, J., Weltevrede, P., Lyne, A.G., Zagkouris, K., Hassall, T.E., Bilous, A.V., Breton, R.P., Falcke, H., Grießmeier, J.-M., Keane, E., Karastergiou, A., Kuniyoshi, M., Noutsos, A., Osłowski, S., Serylak, M., Sobey, C., Ter Veen, S., Alexov, A., Anderson, J., Asgekar, A., Avruch, I.M., Bell, M.E., Bentum, M.J., Bernardi, G., Bîrzan, L., Bonafede, A., Breitling, F., Broderick, J.W., Brüggen, M., Ciardi, B., Corbel, S., De Geus, E., De Jong, A., Deller, A., Duscha, S., Eislöffel, J., Fallows, R.A., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., Gunst, A.W., Hamaker, J.P., Heald, G., Horneffer, A., Jonker, P., Juette, E., Kuper, G., Maat, P., Mann, G., Markoff, S., McFadden, R., McKay-Bukowski, D., Miller-Jones, J.C.A., Nelles, A., Paas, H., Pandey-Pommier, M., Pietka, M., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Rowlinson, A., Schwarz, D., Smirnov, O., Steinmetz, M., Stewart, A., Swinbank, J.D., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, M.C., Van Der Horst, A.J., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wijers, R.A.M.J., Wijnands, R., Wijnholds, S.J., Wucknitz, O., and Zarka, P.
Subjects: Astronomy, Astrophysics::High Energy Astrophysical Phenomena, FOS: Physical sciences, Astrophysics, METIS-321663, Astrophysics::Cosmology and Extragalactic Astrophysics, Low frequency, 01 natural sciences, Radio spectrum, law.invention, Telescope, Radio telescope, [SDU] Sciences of the Universe [physics], stars: neutron, Pulsar, law, pulsars: general, 0103 physical sciences, 010303 astronomy & astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), IR-103184, Solar and Stellar Astrophysics (astro-ph.SR), Physics, High Energy Astrophysical Phenomena (astro-ph.HE), 010308 nuclear & particles physics, Astrophysics::Instrumentation and Methods for Astrophysics, Astronomy and Astrophysics, LOFAR, Astronomy and Astrophysic, Astrophysics - Astrophysics of Galaxies, Interstellar medium, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Astrophysics of Galaxies (astro-ph.GA), ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, Radio frequency, EWI-27451, Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Instrumentation and Methods for Astrophysics
Abstract: LOFAR offers the unique capability of observing pulsars across the 10-240 MHz frequency range with a fractional bandwidth of roughly 50%. This spectral range is well-suited for studying the frequency evolution of pulse profile morphology caused by both intrinsic and extrinsic effects: such as changing emission altitude in the pulsar magnetosphere or scatter broadening by the interstellar medium, respectively. The magnitude of most of these effects increases rapidly towards low frequencies. LOFAR can thus address a number of open questions about the nature of radio pulsar emission and its propagation through the interstellar medium. We present the average pulse profiles of 100 pulsars observed in the two LOFAR frequency bands: High Band (120-167 MHz, 100 profiles) and Low Band (15-62 MHz, 26 profiles). We compare them with Westerbork Synthesis Radio Telescope (WSRT) and Lovell Telescope observations at higher frequencies (350 and1400 MHz) in order to study the profile evolution. The profiles are aligned in absolute phase by folding with a new set of timing solutions from the Lovell Telescope, which we present along with precise dispersion measures obtained with LOFAR. We find that the profile evolution with decreasing radio frequency does not follow a specific trend but, depending on the geometry of the pulsar, new components can enter into, or be hidden from, view. Nonetheless, in general our observations confirm the widening of pulsar profiles at low frequencies, as expected from radius-to-frequency mapping or birefringence theories. We offer this catalog of low-frequency pulsar profiles in a user friendly way via the EPN Database of Pulsar Profiles (http://www.epta.eu.org/epndb/)., Comment: 38 pages, 11 figures, 5 tables, A&A in press, updated with editorial corrections
Published: 2016
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23. The LOFAR pilot surveys for pulsars and fast radio transients

Author: K. Zagkouris, Stefan Oslowski, C. Schrijvers, Michel Tagger, A. Noutsos, Jean-Mathias Grießmeier, John D. Swinbank, Simon Cooper, Dominik J. Schwarz, Rob Fender, P. Zarka, Heino Falcke, Philip Best, V. I. Kondratiev, D. McKay-Bukowski, Charlotte Sobey, Arthur Corstanje, Gerard H. Kuper, Christian Vocks, T. Coenen, M. A. Garrett, Y. Tang, M. Serylak, T. E. Hassall, Oleg Smirnov, Gottfried Mann, Olaf Wucknitz, Anna M. M. Scaife, Jason W. T. Hessels, J. Sluman, Aris Karastergiou, Gianni Bernardi, Mark J. Bentum, Michael Kramer, M. Pilia, George Heald, S. ter Veen, A. W. Gunst, H. Munk, H. J. A. Röttgering, A. S. van Amesfoort, E. de Geus, Satyendra Thoudam, Marcus Brüggen, C. Tasse, Harvey Butcher, John McKean, Emanuela Orru, Casey J. Law, M. Kuniyoshi, Chiara Ferrari, F. Breitling, Annalisa Bonafede, Joeri van Leeuwen, M. Pandey-Pommier, A. Zensus, James M. Anderson, Antonia Rowlinson, Ashish Asgekar, C. Toribio, R. Vermeulen, Joris P. W. Verbiest, Evan Keane, Matthias Hoeft, Vishal Gajjar, Jochen Eislöffel, S. Duscha, H. Paas, A. G. Polatidis, A. Alexov, Rebecca McFadden, Benedetta Ciardi, Stefan J. Wijnholds, J. W. Broderick, Richard Fallows, Wolfgang Reich, B. W. Stappers, A. Renting, F. de Gasperin, Adam T. Deller, W. Frieswijk, Martin Bell, Anna V. Bilous, R. J. van Weeren, I. M. Avruch, E. Juette, Patrick Weltevrede, J. P. Hamaker, A. J. van der Horst, Rene P. Breton, Kapteyn Astronomical Institute, Astronomy, Netherlands Institute for Radio Astronomy (ASTRON), University of Amsterdam [Amsterdam] (UvA), Jodrell Bank Centre for Astrophysics (JBCA), University of Manchester [Manchester], University of Southampton, Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud University [Nijmegen], Max-Planck-Institut für Radioastronomie (MPIFR), Unité Scientifique de la Station de Nançay (USN), 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), 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), University of Oxford, Universität Bielefeld, Leibniz-Institut für Astrophysik Potsdam (AIP), SRON Netherlands Institute for Space Research (SRON), Harvard-Smithsonian Center for Astrophysics (CfA), Harvard University-Smithsonian Institution, University of Edinburgh, Jacobs University [Bremen], Universität Hamburg (UHH), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Thüringer Landessternwarte Tautenburg (TLS), 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), Leiden Observatory [Leiden], Universiteit Leiden, Ruhr-Universität Bochum [Bochum], Astronomical Institute Anton Pannekoek (AI PANNEKOEK), University of Oulu, 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), School of Physics and Astronomy [Southampton], Rhodes University, Grahamstown, 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), ANR-09-JCJC-0001,OPALES(2009), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), High Energy Astrophys. & Astropart. Phys (API, FNWI), Radboud university [Nijmegen], 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, 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), 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), Jodrell Bank Centre for Astrophysics, 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), PSL Research University (PSL)-PSL Research University (PSL)-Centre National d’Études Spatiales [Paris] (CNES), Smithsonian Institution-Harvard University [Cambridge], 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), 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), ANR-09-JCJC-0001,OPALES,nOn-thermal Processes in gALaxy cluStErs(2009), Coenen, Thij, Van Leeuwen, Joeri, Hessels, Jason W. T., Stappers, Ben W., Kondratiev, Vladislav I., Alexov, A., Breton, R.P., Bilous, A., Cooper, S., Falcke, H., Fallows, R.A., Gajjar, V., Grießmeier, J.-M., Hassall, T.E., Karastergiou, A., Keane, E.F., Kramer, M., Kuniyoshi, M., Noutsos, A., Osłowski, S., Pilia, M., Serylak, M., Schrijvers, C., Sobey, C., Ter Veen, S., Verbiest, J., Weltevrede, P., Wijnholds, S., Zagkouris, K., Van Amesfoort, A.S., Anderson, J., Asgekar, A., Avruch, I.M., Bell, M.E., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Broderick, J., Brüggen, M., Butcher, H.R., Ciardi, B., Corstanje, A., Deller, A., Duscha, S., Eislöffel, J., Fender, R., Ferrari, C., Frieswijk, W., Garrett, M.A., De Gasperin, F., De Geus, E., Gunst, A.W., Hamaker, J.P., Heald, G., Hoeft, M., Van Der Horst, A., Juette, E., Kuper, G., Law, C., Mann, G., McFadden, R., McKay-Bukowski, D., McKean, J.P., Munk, H., Orru, E., Paas, H., Pandey-Pommier, M., Polatidis, A.G., Reich, W., Renting, A., Röttgering, H., Rowlinson, A., Scaife, A.M.M., Schwarz, D., Sluman, J., Smirnov, O., Swinbank, J., Tagger, M., Tang, Y., Tasse, C., Thoudam, S., Toribio, C., Vermeulen, R., Vocks, C., Van Weeren, R.J., Wucknitz, O., Zarka, P., and Zensus, A.
Subjects: EWI-25426, Aperture array, media_common.quotation_subject, Astronomy, Pilot survey, SPECTRAL INDEX, FOS: Physical sciences, Astrophysics, general [pulsars], METIS-309729, MHZ, Pulsar, surveys, pulsars: general, BURSTS, Survey, Telescope, POPULATION, Solar and Stellar Astrophysics (astro-ph.SR), media_common, Physics, High Energy Astrophysical Phenomena (astro-ph.HE), [PHYS]Physics [physics], ORIGIN, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Astronomy and Astrophysics, telescopes, BINARY, LOFAR, Astronomy and Astrophysic, IR-93231, Astrophysics - Solar and Stellar Astrophysics, Sky, Space and Planetary Science, DISCOVERY, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, STATE CHANGE, Antenna (radio), ALLEN TELESCOPE ARRAY, EMISSION, [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph], Astrophysics - High Energy Astrophysical Phenomena
Abstract: We have conducted two pilot surveys for radio pulsars and fast transients with the Low-Frequency Array (LOFAR) around 140 MHz and here report on the first low-frequency fast-radio burst limit and the discovery of two new pulsars. The first survey, the LOFAR Pilot Pulsar Survey (LPPS), observed a large fraction of the northern sky, ~1.4 x 10^4 sq. deg, with 1-hr dwell times. Each observation covered ~75 sq. deg using 7 independent fields formed by incoherently summing the high-band antenna fields. The second pilot survey, the LOFAR Tied-Array Survey (LOTAS), spanned ~600 sq. deg, with roughly a 5-fold increase in sensitivity compared with LPPS. Using a coherent sum of the 6 LOFAR "Superterp" stations, we formed 19 tied-array beams, together covering 4 sq. deg per pointing. From LPPS we derive a limit on the occurrence, at 142 MHz, of dispersed radio bursts of < 150 /day/sky, for bursts brighter than S > 107 Jy for the narrowest searched burst duration of 0.66 ms. In LPPS, we re-detected 65 previously known pulsars. LOTAS discovered two pulsars, the first with LOFAR or any digital aperture array. LOTAS also re-detected 27 previously known pulsars. These pilot studies show that LOFAR can efficiently carry out all-sky surveys for pulsars and fast transients, and they set the stage for further surveying efforts using LOFAR and the planned low-frequency component of the Square Kilometer Array., 18 pages, 10 figures, accepted for A&A
Published: 2014
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24. 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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25. Differential frequency-dependent delay from the pulsar magnetosphere

Author: Jason W. T. Hessels, Tim Hassall, K. Zagkouris, Patrick Weltevrede, M. A. Garrett, Wilfred Frieswijk, F. de Gasperin, Y. Tang, P. Maat, Martin Bell, Jochen Eislöffel, R. Vermeulen, M. J. Norden, George Heald, Charlotte Sobey, F. Batejat, Chiara Ferrari, Jean-Mathias Griessmeier, James Miller-Jones, Ashish Asgekar, Mark J. Bentum, John McKean, Matthias Hoeft, Michael W. Wise, Gianni Bernardi, Heino Falcke, Michael Kramer, M. Pilia, R. J. van Weeren, M. Serylak, Annalisa Bonafede, C. Tasse, Harvey Butcher, Richard Fallows, J. W. Broderick, A. Alexov, J.-P. de Reijer, V. I. Kondratiev, P. Zarka, M. Pandey-Pommier, Stefan J. Wijnholds, E. Juette, A. W. Gunst, B. Ciardi, Philip Best, Rob Fender, A. Noutsos, Sarod Yatawatta, T. Coenen, H. J. A. Röttgering, M. Kuniyoshi, Ben Stappers, A. Karastergiou, W. Reich, A. G. Polatidis, Olaf Wucknitz, Evan Keane, S. Duscha, F. Breitling, J. Sluman, Roberto Pizzo, Marcus Brüggen, J. van Leeuwen, Hassall, T.E., Stappers, B.W., Weltevrede, P., Hessels, J.W.T., Alexov, A., Coenen, T., Karastergiou, A., Kramer, M., Keane, E.F., Kondratiev, V.I., Van Leeuwen, J., Noutsos, A., Pilia, M., Serylak, M., Sobey, C., Zagkouris, K., Fender, R., Bell, M.E., Broderick, J., Eislöffel, J., Falcke, H., Grießmeier, J.-M., Kuniyoshi, M., Miller-Jones, J.C.A., Wise, M.W., Wucknitz, O., Zarka, P., Asgekar, A., Batejat, F., Bentum, M.J., Bernardi, G., Best, P., Bonafede, A., Breitling, F., Brüggen, M., Butcher, H.R., Ciardi, B., De Gasperin, F., De Reijer, J.-P., Duscha, S., Fallows, R.A., Ferrari, C., Frieswijk, W., Garrett, M.A., Gunst, A.W., Heald, G., Hoeft, M., Juette, E., Maat, P., McKean, J.P., Norden, M.J., Pandey-Pommier, M., Pizzo, R., Polatidis, A.G., Reich, W., Röttgering, H., Sluman, J., Tang, Y., Tasse, C., Vermeulen, R., Van Weeren, R.J., Wijnholds, S.J., Yatawatta, S., High Energy Astrophys. & Astropart. Phys (API, FNWI), University of Southampton, Jodrell Bank Centre for Astrophysics, University of Manchester [Manchester], University of Amsterdam [Amsterdam] (UvA), Netherlands Institute for Radio Astronomy (ASTRON), Oxford Astrophysics, University of Oxford [Oxford], Max-Planck-Institut für Radioastronomie (MPIFR), 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), Thüringer Landessternwarte Tautenburg (TLS), Radboud university [Nijmegen], Astronomical Institute Anton Pannekoek (AI PANNEKOEK), 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), Onsala Space Observatory (OSO), Chalmers University of Technology [Göteborg], Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), 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), University of Edinburgh, Jacobs University [Bremen], Leibniz-Institut für Astrophysik Potsdam (AIP), Universität Hamburg (UHH), Max Planck Institute for Astrophysics, Max-Planck-Gesellschaft, Kapteyn Astronomical Institute [Groningen], University of Groningen [Groningen], Joseph Louis LAGRANGE (LAGRANGE), 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), Leiden Observatory [Leiden], Universiteit Leiden [Leiden], Ruhr-Universität Bochum [Bochum], 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), ANR-09-JCJC-0001,OPALES(2009), European Project: 224838,EC:FP7:PEOPLE,FP7-PEOPLE-2007-4-3-IRG,PULSARS WITH LOFAR(2008), European Project: 267697,EC:FP7:ERC,ERC-2010-AdG_20100224,4PI-SKY(2011), Astronomy, University of Oxford, Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Radboud University [Nijmegen], 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), 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), Universiteit Leiden, École normale supérieure de Lyon (ENS de Lyon)-Université Claude Bernard Lyon 1 (UCBL), and Université de Lyon-Université de Lyon-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
Subjects: IR-89517, POLARIZATION, stellar magnetism, Astronomy, EWI-24496, Magnetosphere, FOS: Physical sciences, Astrophysics, 01 natural sciences, RADIO PULSARS, Pulsar, 0103 physical sciences, Differential (infinitesimal), 010303 astronomy & astrophysics, Telescope, Solar and Stellar Astrophysics (astro-ph.SR), Physics, High Energy Astrophysical Phenomena (astro-ph.HE), DRIFTING SUBPULSES, STABILITY, 010308 nuclear & particles physics, Oscillation, [SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR], Astronomy and Astrophysics, Observable, telescopes, LOFAR, PROFILES, Astronomy and Astrophysic, METIS-302712, Pulse (physics), Pulsars: individual: PSR B0809+74, MODEL, stellar pulsations, Pulsars: general, Astrophysics - Solar and Stellar Astrophysics, Space and Planetary Science, ComputingMethodologies_DOCUMENTANDTEXTPROCESSING, pulsars, stellar rotation, PSR B0809+74, RADIATION, Longitude, Astrophysics - High Energy Astrophysical Phenomena, EMISSION, stellar atmospheres
Abstract: Some radio pulsars show clear drifting subpulses, in which subpulses are seen to drift in pulse longitude in a systematic pattern. Here we examine how the drifting subpulses of PSR B0809+74 evolve with time and observing frequency. We show that the subpulse period (P3) is constant on timescales of days, months and years, and between 14-5100 MHz. Despite this, the shapes of the driftbands change radically with frequency. Previous studies have concluded that, while the subpulses appear to move through the pulse window approximately linearly at low frequencies (< 500 MHz), a discrete step of 180 degrees in subpulse phase is observed at higher frequencies (> 820 MHz) near to the peak of the average pulse profile. We use LOFAR, GMRT, GBT, WSRT and Effelsberg 100-m data to explore the frequency-dependence of this phase step. We show that the size of the subpulse phase step increases gradually, and is observable even at low frequencies. We attribute the subpulse phase step to the presence of two separate driftbands, whose relative arrival times vary with frequency - one driftband arriving 30 pulses earlier at 20 MHz than it does at 1380 MHz, whilst the other arrives simultaneously at all frequencies. The drifting pattern which is observed here cannot be explained by either the rotating carousel model or the surface oscillation model, and could provide new insight into the physical processes happening within the pulsar magnetosphere., 10 pages, 6 figures, accepted for publication in Astronomy and Astrophysics
Published: 2013
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25 results on '"Zagkouris K"'

1. Wide-Band, Low-Frequency Pulse Profiles of 100 Radio Pulsars with LOFAR

2. Pulsar polarisation below 200 MHz: Average profiles and propagation effects

3. The LOFAR Pilot Surveys for Pulsars and Fast Radio Transients

4. Differential Frequency-dependent Delay from the Pulsar Magnetosphere

5. Wide-band Simultaneous Observations of Pulsars: Disentangling Dispersion Measure and Profile Variations

6. A GPU-based survey for millisecond radio transients using ARTEMIS

7. Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

8. Scattering analysis of LOFAR pulsar observations

9. Scattering analysis of LOFAR pulsar observations

10. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

11. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

12. Pulsar polarisation below 200 MHz: Average profiles and propagation effects

13. The LOFAR pilot surveys for pulsars and fast radio transients

14. The LOFAR pilot surveys for pulsars and fast radio transients

15. Differential frequency-dependent delay from the pulsar magnetosphere

16. Differential frequency-dependent delay from the pulsar magnetosphere

17. Differential frequency-dependent delay from the pulsar magnetosphere

18. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

19. Differential frequency-dependent delay from the pulsar magnetosphere

20. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

21. Synchronous X-ray and Radio Mode Switches: A Rapid Global Transformation of the Pulsar Magnetosphere

22. Wide-band, low-frequency pulse profiles of 100 radio pulsars with LOFAR

23. The LOFAR pilot surveys for pulsars and fast radio transients

24. Wide-band simultaneous observations of pulsars: disentangling dispersion measure and profile variations

25. Differential frequency-dependent delay from the pulsar magnetosphere

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25 results on '"Zagkouris K"'

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