On the magnetization of gamma-ray burst blast waves
Abstract
The origin of magnetic fields that permeate the blast waves of gamma-ray bursts (GRBs) is a long-standing problem. The present paper argues that in four GRBs revealing extended emission at >100 MeV, with follow-up in the radio, optical and X-ray domains at later times, this magnetization can be described as the partial decay of the micro-turbulence that is generated in the shock precursor. Assuming that the bulk of the extended emission >100 MeV can be interpreted as synchrotron emission of shock-accelerated electrons, we model the multi-wavelength light curves of GRB 090902B, GRB 090323, GRB 090328 and GRB 110731A, using a simplified then a full synchrotron calculation with power-law-decaying micro-turbulence ɛB ≈ tαt (t denotes the time since injection through the shock, in the comoving blast frame). We find that these models point to a consistent value of the decay exponent -0.5 ≲ αt ≲ -0.4.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- November 2013
- DOI:
- 10.1093/mnras/stt1494
- arXiv:
- arXiv:1305.3689
- Bibcode:
- 2013MNRAS.435.3009L
- Keywords:
-
- acceleration of particles;
- shock waves;
- gamma-ray burst: general;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Physics - Plasma Physics
- E-Print:
- 8 pages, 4 figures - discussion added, conclusions unchanged - version to appear in MNRAS