Zhao, Xiaohong 2013 磁场衰减对伽马暴谱的影响

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Title:		Gamma-Ray Burst Spectrum with Decaying Magnetic Field
Authors:		Zhao, Xiaohong; Li, Zhuo; Liu, Xuewen; Zhang, Bin-bin; Bai, Jinming; Mészáros, Peter
Affiliation:		AA(Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA; zhaoxh@ynao.ac.cn), AB(Department of Astronomy and Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China; zhuo.li@pku.edu.cn), AC(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA ; Department of Physics, Sichuan University, Chengdu 610065, China), AD(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA ; Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA), AE(Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China ; Key Laboratory for the Structure and Evolution of Celestial Bodies, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming, China), AF(Department of Astronomy and Astrophysics and Department of Physics, The Pennsylvania State University, University Park, PA 16802, USA)
Publication:		The Astrophysical Journal, Volume 780, Issue 1, article id. 12, 6 pp. (2014). (ApJ Homepage)
Publication Date:		01/2014
Origin:		IOP
Astronomy Keywords:		gamma-ray burst: general, magnetic fields, radiation mechanisms: non-thermal
DOI:		10.1088/0004-637X/780/1/12
Bibliographic Code:		2014ApJ...780...12Z

Abstract

In the internal shock model for gamma-ray bursts (GRBs), the synchrotron spectrum from the fast cooling electrons in a homogeneous downstream magnetic field (MF) is too soft to produce the low-energy slope of GRB spectra. However, the MF may decay downstream with distance from the shock front. Here we show that the synchrotron spectrum becomes harder if electrons undergo synchrotron and inverse-Compton cooling in a decaying MF. To reconcile this with the typical GRB spectrum with low-energy slope νF _νvpropν, the postshock MF decay time must be comparable to the cooling time of the bulk electrons (corresponding to a MF decaying length typically of ~10⁵ skin depths); that the inverse-Compton cooling should dominate synchrotron cooling after the MF decay time; and/or that the MF decays with comoving time roughly as Bvpropt ^–1.5. An internal shock synchrotron model with a decaying MF can account for the majority of GRBs with low-energy slopes not harder than ν^4/3.

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