Late internal shock model for bright X-ray flares in Gamma-ray Burst afterglows and GRB 011121

Y. Z. Fan; D. M. Wei

doi:10.1111/j.1745-3933.2005.00102.x

paper

Late internal shock model for bright X-ray flares in Gamma-ray Burst afterglows and GRB 011121

arXiv:astro-ph/0506155 · doi:10.1111/j.1745-3933.2005.00102.x

Abstract

We explore two possible models which might give rise to bright X-ray flares in GRBs afterglows. One is an external forward-reverse shock model, in which the shock parameters of forward/reverse shocks are taken to be quite different. The other is a so called "late internal shock model", which requires a refreshed unsteady relativistic outflow generated after the prompt $γ -$ ray emission. In the forward-reverse shock model, after the time $t_{\times}$ at which the RS crosses the ejecta, the flux declines more slowly than $(t_{\oplus} / t_{\times})^{- (2 + β)}$ , where $t_{\oplus}$ denotes the observer's time and $β$ is the spectral index of the X-ray emission. In the ``late internal shock model", decaying slopes much steeper than $(t_{\oplus} / t_{e, \oplus})^{- (2 + β)}$ are possible if the central engine shuts down after $t_{e, \oplus}$ and the observed variability timescale of the X-ray flare is much shorter than $t_{e, \oplus}$ . The sharp decline of the X-ray flares detected in GRB 011121, XRF 050406, GRB 050502b, and GRB 050730 rules out the external forward-reverse shock model directly and favors the "late internal shock model". These X-ray flares could thus hint that the central engine operates again and a new unsteady relativistic outflow is generated just a few minutes after the intrinsic hard burst.

6 pages (2 figure), submitted to MNRAS Letters on 05/19/2005, accepted for publication on 09/01/2005. Major revision

Late internal shock model for bright X-ray flares in Gamma-ray Burst afterglows and GRB 011121

Abstract

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