A comprehensive radio view of the extremely bright gamma-ray burst 130427A
- A. J. van der Horst1,★,
- Z. Paragi2,
- A. G. de Bruyn3,4,
- J. Granot5,
- C. Kouveliotou6,
- K. Wiersema7,
- R. L. C. Starling7,
- P. A. Curran8,
- R. A. M. J. Wijers1,
- A. Rowlinson1,
- G. A. Anderson9,10,
- R. P. Fender9,10,
- J. Yang2,11 and
- R. G. Strom3
- 1Anton Pannekoek Institute, University of Amsterdam, Science Park 904, NL-1098 XH Amsterdam, the Netherlands
- 2Joint Institute for VLBI in Europe, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
- 3ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, NL-7990 AA Dwingeloo, the Netherlands
- 4Kapteyn Astronomical Institute, PO Box 800, NL-9700 AV Groningen, the Netherlands
- 5Departement of Natural Sciences, The Open University of Israel, PO Box 808, Ra'anana 43537, Israel
- 6Space Science Office, ZP12, NASA/Marshall Space Flight Center, Huntsville, AL 35812, USA
- 7Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
- 8International Centre for Radio Astronomy Research − Curtin University, GPO Box U1987, Perth, WA 6845, Australia
- 9Department of Physics, Astrophysics, University of Oxford, Denys Wilkinson Building, Oxford OX1 3RH, UK
- 10School of Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, UK
- 11Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, SE-43992 Onsala, Sweden
- ↵★E-mail: A.J.vanderHorst{at}uva.nl
- Accepted 2014 August 12.
- Received 2014 August 12.
- In original form 2014 April 4.
- First published online September 15, 2014.
Abstract
GRB 130427A was extremely bright as a result of occurring at low redshift whilst the energetics were more typical of high-redshift gamma-ray bursts (GRBs). We collected well-sampled light curves at 1.4 and 4.8 GHz of GRB 130427A with the Westerbork Synthesis Radio Telescope (WSRT); and we obtained its most accurate position with the European Very Long Baseline Interferometry Network (EVN). Our flux density measurements are combined with all the data available at radio, optical and X-ray frequencies to perform broad-band modelling in the framework of a reverse–forward shock model and a two-component jet model, and we discuss the implications and limitations of both models. The low density inferred from the modelling implies that the GRB 130427A progenitor is either a very low metallicity Wolf–Rayet star, or a rapidly rotating, low-metallicity O star. We also find that the fraction of the energy in electrons is evolving over time, and that the fraction of electrons participating in a relativistic power-law energy distribution is less than 15 per cent. We observed intraday variability during the earliest WSRT observations, and the source sizes inferred from our modelling are consistent with this variability being due to interstellar scintillation effects. Finally, we present and discuss our limits on the linear and circular polarization, which are among the deepest limits of GRB radio polarization to date.
Key words
- © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
