Spectral evolution and the onset of the X-ray GRB afterglow
High Energy Astrophysical Phenomena
2015-05-27 v1
Abstract
Based on light curves from the Swift Burst Analyser, we investigate whether a `dip' feature commonly seen in the early-time hardness ratios of Swift-XRT data could arise from the juxtaposition of the decaying prompt emission and rising afterglow. We are able to model the dip as such a feature, assuming the afterglow rises as predicted by Sari & Piran (1999). Using this model we measure the initial bulk Lorentz factor of the fireball. For a sample of 23 GRBs we find a median value of Gamma_0=225, assuming a constant-density circumburst medium; or Gamma_0=93 if we assume a wind-like medium.
Keywords
Cite
@article{arxiv.1101.5923,
title = {Spectral evolution and the onset of the X-ray GRB afterglow},
author = {P. A. Evans and J. P. Osborne and R. Willingale and P. T. O'Brien},
journal= {arXiv preprint arXiv:1101.5923},
year = {2015}
}
Comments
4 pages, 3 figures. To appear in the proceedings of GRB 2010, Annapolis November 2010. (AIP Conference proceedings)