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Clark CJ, Kerr M, Barr ED, Bhattacharyya B, Breton RP, Bruel P, Camilo F, Chen W, Cognard I, Cromartie HT, Deneva J, Dhillon VS, Guillemot L, Kennedy MR, Kramer M, Lyne AG, Sánchez DM, Nieder L, Phillips C, Ransom SM, Ray PS, Roberts MSE, Roy J, Smith DA, Spiewak R, Stappers BW, Tabassum S, Theureau G, Voisin G. Neutron star mass estimates from gamma-ray eclipses in spider millisecond pulsar binaries. Nat Astron 2023; 7:451-462. [PMID: 37096051 PMCID: PMC10119022 DOI: 10.1038/s41550-022-01874-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 12/01/2022] [Indexed: 05/03/2023]
Abstract
Reliable neutron star mass measurements are key to determining the equation of state of cold nuclear matter, but such measurements are rare. Black widows and redbacks are compact binaries consisting of millisecond pulsars and semi-degenerate companion stars. Spectroscopy of the optically bright companions can determine their radial velocities, providing inclination-dependent pulsar mass estimates. Although inclinations can be inferred from subtle features in optical light curves, such estimates may be systematically biased due to incomplete heating models and poorly understood variability. Using data from the Fermi Large Area Telescope, we have searched for gamma-ray eclipses from 49 spider systems, discovering significant eclipses in 7 systems, including the prototypical black widow PSR B1957+20. Gamma-ray eclipses require direct occultation of the pulsar by the companion, and so the detection, or significant exclusion, of a gamma-ray eclipse strictly limits the binary inclination angle, providing new robust, model-independent pulsar mass constraints. For PSR B1957+20, the eclipse implies a much lighter pulsar (1.81 ± 0.07 solar masses) than inferred from optical light curve modelling.
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Affiliation(s)
- C. J. Clark
- Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Hannover, Germany
- Leibniz Universität Hannover, Hannover, Germany
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - M. Kerr
- Space Science Division, Naval Research Laboratory, Washington, DC USA
| | - E. D. Barr
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - B. Bhattacharyya
- National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India
| | - R. P. Breton
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - P. Bruel
- Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, Palaiseau, France
| | - F. Camilo
- South African Radio Astronomy Observatory, Cape Town, South Africa
| | - W. Chen
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - I. Cognard
- Laboratoire de Physique et Chimie de l’Environnement et de l’Espace–Université d’Orléans, CNRS, Orléans, France
- Observatoire Radioastronomique de Nançay, Observatoire de Paris, Université PSL, Université d’Orléans, CNRS, Nançay, France
| | - H. T. Cromartie
- Cornell Center for Astrophysics and Planetary Science and Department of Astronomy, Cornell University, Ithaca, NY USA
| | - J. Deneva
- Space Science Division, Naval Research Laboratory, Washington, DC USA
- College of Science, George Mason University, Fairfax, VA USA
| | - V. S. Dhillon
- Department of Physics and Astronomy, University of Sheffield, Sheffield, UK
- Instituto de Astrofísica de Canarias, La Laguna, Spain
| | - L. Guillemot
- Laboratoire de Physique et Chimie de l’Environnement et de l’Espace–Université d’Orléans, CNRS, Orléans, France
- Observatoire Radioastronomique de Nançay, Observatoire de Paris, Université PSL, Université d’Orléans, CNRS, Nançay, France
| | - M. R. Kennedy
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- Department of Physics, University College Cork, Cork, Ireland
| | - M. Kramer
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- Max-Planck-Institut für Radioastronomie, Bonn, Germany
| | - A. G. Lyne
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - D. Mata Sánchez
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- Instituto de Astrofísica de Canarias, La Laguna, Spain
- Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Spain
| | - L. Nieder
- Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Hannover, Germany
- Leibniz Universität Hannover, Hannover, Germany
| | - C. Phillips
- University of Virginia, Charlottesville, VA USA
| | - S. M. Ransom
- National Radio Astronomy Observatory, Socorro, NM USA
| | - P. S. Ray
- Space Science Division, Naval Research Laboratory, Washington, DC USA
| | | | - J. Roy
- National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune, India
| | - D. A. Smith
- Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, Pessac, France
| | - R. Spiewak
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria Australia
- Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria Australia
| | - B. W. Stappers
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
| | - S. Tabassum
- New York University Abu Dhabi, Abu Dhabi, United Arab Emirates
- Department of Physics and Astronomy, West Virginia University, Morgantown, WV USA
| | - G. Theureau
- Laboratoire de Physique et Chimie de l’Environnement et de l’Espace–Université d’Orléans, CNRS, Orléans, France
- Observatoire Radioastronomique de Nançay, Observatoire de Paris, Université PSL, Université d’Orléans, CNRS, Nançay, France
- Laboratoire Univers et Théories, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Meudon, France
| | - G. Voisin
- Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, The University of Manchester, Manchester, UK
- Laboratoire Univers et Théories, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Meudon, France
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Broderick JW, Fender RP, Breton RP, Stewart AJ, Rowlinson A, Swinbank JD, Hessels JWT, Staley TD, van der Horst AJ, Bell ME, Carbone D, Cendes Y, Corbel S, Eislöffel J, Falcke H, Grießmeier JM, Hassall TE, Jonker P, Kramer M, Kuniyoshi M, Law CJ, Markoff S, Molenaar GJ, Pietka M, Scheers LHA, Serylak M, Stappers BW, Ter Veen S, van Leeuwen J, Wijers RAMJ, Wijnands R, Wise MW, Zarka P. Low-radio-frequency eclipses of the redback pulsar J2215+5135 observed in the image plane with LOFAR. Mon Not R Astron Soc 2016; 459:2681-2689. [PMID: 27279782 DOI: 10.1093/mnras/stw794] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/27/2015] [Revised: 03/27/2016] [Accepted: 04/05/2016] [Indexed: 06/06/2023]
Abstract
The eclipses of certain types of binary millisecond pulsars (i.e. 'black widows' and 'redbacks') are often studied using high-time-resolution, 'beamformed' radio observations. However, they may also be detected in images generated from interferometric data. As part of a larger imaging project to characterize the variable and transient sky at radio frequencies <200 MHz, we have blindly detected the redback system PSR J2215+5135 as a variable source of interest with the Low-Frequency Array (LOFAR). Using observations with cadences of two weeks - six months, we find preliminary evidence that the eclipse duration is frequency dependent (∝ν-0.4), such that the pulsar is eclipsed for longer at lower frequencies, in broad agreement with beamformed studies of other similar sources. Furthermore, the detection of the eclipses in imaging data suggests an eclipsing medium that absorbs the pulsed emission, rather than scattering it. Our study is also a demonstration of the prospects of finding pulsars in wide-field imaging surveys with the current generation of low-frequency radio telescopes.
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Affiliation(s)
- J W Broderick
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK; ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - R P Fender
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - R P Breton
- Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - A J Stewart
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - A Rowlinson
- ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - J D Swinbank
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - J W T Hessels
- ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - T D Staley
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - A J van der Horst
- Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC 20052, USA
| | - M E Bell
- CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia; ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), The University of Sydney, NSW 2006, Australia
| | - D Carbone
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - Y Cendes
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - S Corbel
- Laboratoire AIM (CEA/IRFU - CNRS/INSU - Université Paris Diderot), CEA DSM/IRFU/SAp, F-91191 Gif-sur-Yvette, France; Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 - Univ. Orléans, OSUC, F-18330 Nançay, France
| | - J Eislöffel
- Thüringer Landessternwarte, Sternwarte 5, D-07778 Tautenburg, Germany
| | - H Falcke
- Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands; ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - J-M Grießmeier
- LPC2E - Université d'Orléans/CNRS, F-45071 Orléans cedex 2, France; Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 - Univ. Orléans, OSUC, F-18330 Nançay, France
| | - T E Hassall
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - P Jonker
- SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584 CA Utrecht, the Netherlands; Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands
| | - M Kramer
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
| | - M Kuniyoshi
- NAOJ Chile Observatory, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
| | - C J Law
- Department of Astronomy and Radio Astronomy Lab, University of California, Berkeley, CA, USA
| | - S Markoff
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - G J Molenaar
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands; Department of Physics and Electronics, Rhodes University, PO Box 94, Grahamstown 6140 South Africa
| | - M Pietka
- Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - L H A Scheers
- Centrum Wiskunde and Informatica, Science Park 123, NL-1098 XG Amsterdam, the Netherlands; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - M Serylak
- Department of Physics and Astronomy, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa; SKA South Africa, 3rd Floor, The Park, Park Road, Pinelands 7405, South Africa
| | - B W Stappers
- Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
| | - S Ter Veen
- ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - J van Leeuwen
- ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - R A M J Wijers
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - R Wijnands
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - M W Wise
- ASTRON, the Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands; Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
| | - P Zarka
- LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, F-92195 Meudon, France; Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 - Univ. Orléans, OSUC, F-18330 Nançay, France
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3
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Carbone D, van der Horst AJ, Wijers RAMJ, Swinbank JD, Rowlinson A, Broderick JW, Cendes YN, Stewart AJ, Bell ME, Breton RP, Corbel S, Eislöffel J, Fender RP, Grießmeier JM, Hessels JWT, Jonker P, Kramer M, Law CJ, Miller-Jones JCA, Pietka M, Scheers LHA, Stappers BW, van Leeuwen J, Wijnands R, Wise M, Zarka P. New methods to constrain the radio transient rate: results from a survey of four fields with LOFAR. Mon Not R Astron Soc 2016; 459:3161-3174. [PMID: 27279785 DOI: 10.1093/mnras/stw539] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2014] [Revised: 02/29/2016] [Accepted: 03/03/2016] [Indexed: 06/06/2023]
Abstract
We report on the results of a search for radio transients between 115 and 190 MHz with the LOw-Frequency ARray (LOFAR). Four fields have been monitored with cadences between 15 min and several months. A total of 151 images were obtained, giving a total survey area of 2275 deg2. We analysed our data using standard LOFAR tools and searched for radio transients using the LOFAR Transients Pipeline. No credible radio transient candidate has been detected; however, we are able to set upper limits on the surface density of radio transient sources at low radio frequencies. We also show that low-frequency radio surveys are more sensitive to steep-spectrum coherent transient sources than GHz radio surveys. We used two new statistical methods to determine the upper limits on the transient surface density. One is free of assumptions on the flux distribution of the sources, while the other assumes a power-law distribution in flux and sets more stringent constraints on the transient surface density. Both of these methods provide better constraints than the approach used in previous works. The best value for the upper limit we can set for the transient surface density, using the method assuming a power-law flux distribution, is 1.3 × 10-3 deg-2 for transients brighter than 0.3 Jy with a time-scale of 15 min, at a frequency of 150 MHz. We also calculated for the first time upper limits for the transient surface density for transients of different time-scales. We find that the results can differ by orders of magnitude from previously reported, simplified estimates.
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Affiliation(s)
- D Carbone
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands
| | - A J van der Horst
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; Department of Physics, The George Washington University, 725 21 Street NW, Washington, DC 20052, USA
| | - R A M J Wijers
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands
| | - J D Swinbank
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
| | - A Rowlinson
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia; ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - J W Broderick
- ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands; Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK; Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ, UK
| | - Y N Cendes
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands
| | - A J Stewart
- Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
| | - M E Bell
- CSIRO Australia Telescope National Facility, PO Box 76, Epping NSW 1710, Australia; ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), The University of Sydney, NSW 2006, Australia
| | - R P Breton
- Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
| | - S Corbel
- Laboratoire AIM (CEA/IRFU - CNRS/INSU - Université Paris Diderot), CEA DSM/IRFU/SAp, F-91191 Gif-sur-Yvette, France; Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 - Univ. Orléans, OSUC, F-18330 Nançay, France
| | - J Eislöffel
- Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany
| | - R P Fender
- Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
| | - J-M Grießmeier
- Station de Radioastronomie de Nançay, Observatoire de Paris, CNRS/INSU, USR 704 - Univ. Orléans, OSUC, F-18330 Nançay, France; Laboratoire de Physique et Chimie de l'Environnement et de l'Espace, LPC2E UMR 7328 CNRS, F-45071 Orléans, France
| | - J W T Hessels
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - P Jonker
- SRON, Netherlands Institute for Space Research, Sorbonnelaan 2, NL-3584-CA Utrecht, the Netherlands; Department of Astrophysics/IMAPP, Radboud University Nijmegen, PO Box 9010, NL-6500 GL Nijmegen, the Netherlands
| | - M Kramer
- Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK; Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
| | - C J Law
- Department of Astronomy and Radio Astronomy Lab, University of California, Berkeley, CA, USA
| | - J C A Miller-Jones
- International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
| | - M Pietka
- Oxford Astrophysics, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
| | - L H A Scheers
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; Centrum Wiskunde & Informatica, PO Box 94079, NL-1090 GB Amsterdam, the Netherlands
| | - B W Stappers
- Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester M13 9PL, UK
| | - J van Leeuwen
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - R Wijnands
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands
| | - M Wise
- Anton Pannekoek Institute for Astronomy, University of Amsterdam, Postbus 94249, NL-1090 GE Amsterdam, the Netherlands; ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
| | - P Zarka
- LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, F-92195 Meudon, France
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