Toma 2009 Cocoon的X射线做种子光子解释高能GeV辐射

主要内容:
基于080916C的观测, 总结出五个高能的观测特点(是否是普遍特点还有待进一步证实):
1. 从8keV到13GeV, 可以用简单的broken power law拟合；
2. 高能的光子比MeV的晚5秒左右到(但不是spectral time lag)；
3. 当考虑高能光子的时候, 时间向后移(也就是spectral time lag, 如果没理解错的话)；
4. 大于100MeV的光子比低能的持续更长时间, 对080916C来说, 高能的到了1400s, 低能的不到200s；
5. E_iso~1e55 erg, 很亮.

模型:
高能来自于EIC. Cocoon是恒星爆炸时候产生的一个张角更大光深更大但速度更慢的喷流, 可以产生X射线作为种子光子, 被内激波的相对论电子散射到GeV, 就是观测到的高能辐射了.

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Title:		An up-scattered cocoon emission model of Gamma-Ray Burst high-energy lags
Authors:		Toma, Kenji; Wu, Xue-Feng; Meszaros, Peter
Publication:		eprint arXiv:0905.1697
Publication Date:		05/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Comment:		emulateapj 14 pages, 5 figures, submitted to ApJ
Bibliographic Code:		2009arXiv0905.1697T

Abstract

The Fermi Gamma-ray Space Telescope recently detected the most energetic gamma-ray burst so far, GRB 080916C, and reported its detailed temporal properties in an extremely broad spectral range: (i) the time-resolved spectra are well described by broken power-law forms over the energy range of $10 {\rm keV}-10$ GeV, (ii) the high-energy emission (at $\epsilon > 100$ MeV) is delayed by $\approx 5$s with respect to the $\epsilon \lesssim 1$ MeV emission, and (iii) the higher energy fluxes have the later onset times. We show that this behavior of the high-energy emission can be explained by a model in which the prompt emission consists of two components: one is the emission component peaking at $\epsilon \sim 1$ MeV due to the synchrotron-self-Compton radiation of electrons accelerated in the internal shock of the jet and the other is the component peaking at $\epsilon \sim 100$ MeV due to up-scattering of the photospheric X-ray emission of the expanding cocoon (i.e., the hot bubble produced by dissipation of the jet energy inside the progenitor star) off the same electrons in the jet. Based on this model, we derive some constraints on the radius of the progenitor star and the total energy and mass of the cocoon of this GRB, which may provide information on the structure of the progenitor star and the physical conditions of the jet propagating in the star. We discuss some predictions of this model, including a prompt bright optical emission and a soft X-ray excess.

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