2018/01/28 by Q. Zhang, S. L. Xiong, Zhang, Q. +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #astro-ph.HE
paper · pdf · doi:10.48550/arxiv.1801.10032
8 pages, 1 figure, submitted to ApJ. arXiv admin note: substantial text overlap with arXiv:1801.08258. We have combined both works into a single paper (see arXiv: 1801.08258v2)
arxiv created 2018/03/08 · arxiv updated 2018/03/09
Electrons accelerated in relativistic collisionless shocks are usually assumed to follow a power-law energy distribution with an index of p. Observationally, although most gamma-ray bursts (GRBs) have afterglows that are consistent with p>2, there are still a few GRBs suggestive of a hard (p<2) electron energy spectrum. Our previous works found strong evidence for the exist of a double power-law hard electron energy (DPLH) spectrum with 1<p1<2, p2>2 and an injection break assumed as γ\rm b∝ γq in the relativistic regime. Moreover, these works suggested a possibly universal value of q∼0.5. GRB~060908 is another case that shows a flat spectrum in the optical/near-infrared band and requires a hard electron energy distribution, which, along with the rich multi-band afterglow data, provides us an opportunity to test this conjecture. Based on the model of \citetResmi08, we explain the multi-band afterglow of GRB~060908 in a wind medium and take also the synchrotron self-Compton effect. We show that though the DPLH spectrum is favored by the afterglow data, the value of q is badly constrained due to the relatively large uncertainties of the spectral indices. However, the afterglow can be well reproduced if we adopt q=0.5, implying the compatibility of the above conjecture with the data.