Lazzati 2009 光球辐射可以效率很高

主要内容:
数值模拟, 不过这个结论是容易理解的, 主要光学薄半径和coasting半径相当, 就可以辐射效率很高了.

但是有个问题是光球辐射是黑体谱, 怎么转换成观测到的非热谱呢? 文中给了点儿定性的解释, 说是康普顿散射.

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Title:		Very high efficiency photospheric emission in long duration gamma-ray bursts
Authors:		Lazzati, Davide; Morsony, Brian J.; Begelman, Mitch
Publication:		eprint arXiv:0904.2779
Publication Date:		04/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		4 pages, uses emulateapj and apjfonts (both included). 4 color figures. Submitted to ApJL
Bibliographic Code:		2009arXiv0904.2779L

Abstract

We numerically analyze the evolution of a long-duration gamma-ray burst jet as it leaves the progenitor star and propagates to the photospheric radius, where radiation can be released. We find that the interaction of the relativistic material with the progenitor star has influences well beyond the stellar surface. Tangential collimation shocks are observed throughout the jet evolution, out to about 100 stellar radii, which is the whole range of our simulation. We find that the jet is internally hot at the photospheric radius and we compute the photospheric emission. The photosphere is a very efficient radiator, capable of converting more than half of the total energy of the jet into radiation. We show that bright photospheres are a common feature of jets born inside massive progenitor stars and that this effect can explain the high radiative efficiency observed in long-duration bursts.

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