Bosnjak 2008 数值计算内激波的高能辐射

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数值计算和解析结果比较, 发现相差很大, 解析结果估计过高

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Title:		Prompt high-energy emission from gamma-ray bursts in the internal shock model
Authors:		Bosnjak, Z.; Daigne, F.; Dubus, G.
Publication:		eprint arXiv:0811.2956
Publication Date:		11/2008
Origin:		ARXIV
Keywords:		Astrophysics
Comment:		27 pages, 20 figures, submitted to A&A
Bibliographic Code:		2008arXiv0811.2956B

Abstract

The prompt GRB emission is thought to arise from electrons accelerated in internal shocks propagating within a highly relativistic outflow. The launch of Fermi offers the prospect of observations with unprecedented sensitivity in high-energy (>100 MeV) gamma-rays. The aim is to explore the predictions for HE emission from internal shocks, taking into account both dynamical and radiative aspects, and to deduce how HE observations constrain the properties of the relativistic outflow. The emission is modeled by combining a time-dependent radiative code with a dynamical code giving the evolution of the physical conditions in the shocked regions.Synthetic lightcurves and spectra are compared to observations. The HE emission deviates significantly from analytical estimates, which tend to overpredict the IC component, when the time dependence and full cross-sections are included. The exploration of the parameter space favors the case where the dominant process in the BATSE range is synchrotron emission. The HE component becomes stronger for weaker magnetic fields. The HE lightcurve can display a prolonged pulse duration due to IC emission, or even a delayed peak compared to the BATSE range.Alternatively, having dominant IC emission in the BATSE range requires most electrons to be accelerated into a steep power-law distribution and implies strong 2nd order IC scattering. In this case, the BATSE and HE lightcurves are very similar. The combined dynamical and radiative approach allows a firm appraisal of GRB HE prompt emission. A diagnostic procedure is presented to identify from observations the dominant emission process and derive constrains on the bulk Lorentz factor, particle density and magnetic field of the outflow.

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