Beloborodov, A. M. 2010 是否伽马暴余辉本身的辐射就不是各向同性的

主要内容:
一般理论说余辉在共动系里还是各向同性的。各向同性会抹平任何快速的光变（这个没懂）。不过像同步辐射实际上是各向异性的，如果是的话，可以解释观测到的X射线的快速光变，还有耀发，以及喷流拐折将比较难观测到。

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Title:		Is GRB afterglow emission intrinsically anisotropic ?
Authors:		Beloborodov, A. M.; Daigne, F.; Mochkovitch, R.; Uhm, Z. L.
Publication:		eprint arXiv:1003.1265
Publication Date:		03/2010
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Extragalactic Astrophysics
Comment:		13 pages, 5 figures, submitted to MNRAS
Bibliographic Code:		2010arXiv1003.1265B

Abstract

The curvature of a relativistic blast wave implies that its emission arrives to observers with a spread in time. This effect is believed to wash out any fast variability in the lightcurves of GRB afterglows. We note that the spreading effect is reduced if emission is anisotropic in the rest-frame of the blast wave (i.e. if emission is limb-brightened or limb-darkened). In particular, synchrotron emission is almost certainly anisotropic, and may be strongly anisotropic, depending on details of electron acceleration in the blast wave. Anisotropic afterglows can display fast and strong variability at high frequencies (above the 'fast-cooling' frequency). This may explain the existence of bizarre features in the X-ray afterglows of GRBs, such as sudden drops and flares. We also note that a moderate anisotropy can significantly delay the 'jet break' in the lightcurve, which makes it harder to detect.

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