Zou 2009 早期外激波的辐射限制罗仑兹因子

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另外还和其它方法进行了比较. 不是很一致.

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Title:		Lorentz Factor Constraint from the very early external shock of the gamma-ray burst ejecta
Authors:		Zou, Yuan-Chuan; Piran, Tsvi
Publication:		eprint arXiv:0908.4418
Publication Date:		08/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		9 pages, 2 figures. Submitted to MNRAS
Bibliographic Code:		2009arXiv0908.4418Z

Abstract

While it is generally agreed that the emitting regions in Gamma-Ray Bursts (GRBs) move ultra relativistically towards the observer, different estimates of the initial Lorentz factors, $\Gamma_0$, lead to different, at times conflicting estimates. We show here that the quiet periods in which the signals goes down below the instrumental thresholds, put strong upper limits on the values of $\Gamma_0$. According to the standard internal-external shocks model an external shock should develop during the prompt stage. This external shock radiates in the hard X-rays to soft gamma-rays bands and this emission should be seen as a smooth background signal. The observed deep minima indicate that this contribution is negligible. This limits, in turn, $\Gamma_0$. We obtain upper limits on $\Gamma_0$ for several bursts with typical values around hundreds. We compare these values with those obtained by the other methods, which typically yield lower limits. The results are marginally consistent leaving only a narrow range of allowed values for $\Gamma_0$.

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