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arXiv 1709.05899astro-ph.HE
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冷却电子产生的伽马射线暴的低能能谱

Low-energy Spectra of Gamma-ray Bursts from Cooling Electrons

Jin-Jun Geng, Yong-Feng Huang, Xue-Feng Wu, Bing Zhang, Hong-Shi Zong

摘要:

伽马射线暴瞬发辐射的低能谱与电子的能量分布密切相关,而电子的能量分布又受其冷却过程的调节。我们开发了一个数值程序来计算在给定的初始参数下电子分布的演化,其中三个冷却过程(即,绝热、同步加速和逆康普顿冷却)和衰减磁场的影响。通过探索火球和坡印廷通量主导制度的合理参数空间的结果序列。可以识别电子的不同冷却模式,并且它们具有特定的主导冷却机制。我们的研究结果表明,硬化的低能谱可以归因于同步自康普顿冷却内的内部冲击模型的主导地位,或衰减的同步冷却内的坡印亭通量占主导地位的射流的情况。这两种机制可以通过观察某些伽玛暴中孤立短脉冲的硬低能谱来区分。当喷出物以极端的相对论速度运动时,绝热冷却的优势也会导致硬低能谱。从时间分辨低能谱的信息可以帮助探测伽玛暴喷出物的物理特性,通过我们的数值计算结果。

英文摘要:

The low-energy spectra of gamma-ray bursts' (GRBs) prompt emission are closely related to the energy distribution of electrons, which is further regulated by their cooling processes. We develop a numerical code to calculate the evolution of the electron distribution with given initial parameters, in which three cooling processes (i.e., adiabatic, synchrotron and inverse Compton cooling) and the effect of decaying magnetic field are coherently considered. A sequence of results are presented by exploring the plausible parameter space for both the fireball and the Poynting-flux-dominated regime. Different cooling patterns for the electrons can be identified and they are featured by a specific dominant cooling mechanism. Our results show that the hardening of the low-energy spectra can be attributed to the dominance of synchrotron self-Compton cooling within the internal shock model, or to decaying synchrotron cooling within the Poynting-flux-dominated jet scenario. These two mechanisms can be distinguished by observing the hard low-energy spectra of isolated short pulses in some GRBs. The dominance of adiabatic cooling can also lead to hard low-energy spectra when the ejecta is moving at an extreme relativistic speed. The information from the time-resolved low-energy spectra can help to probe the physical characteristics of the GRB ejecta via our numerical results.

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