Nakar 2009 同步和SSC的Klein-Nishina效应

主要内容:
本文只考虑了KN区不会有正负电子对产生的情况(光深小). (对伽玛暴来说可能性比较小.)

精彩摘抄:
这是文中弱KN效应的图: 黑线是同步和SSC的谱(红线是数值结果), 虚线是不考虑KN应该出现的谱. SSC部分容易理解, 同步部分, 可能原因是由于较高频率处的光子被KN抑制了, 所以比不考虑KN的时候多一些. (可是我印象中这点差别很小的, 特别是光深也很小的时候, 只有\tau的光子被IC, 而这里确相差有几倍的样子, 不知道什么原因. 也没仔细看文中的解释.)

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Title:		Klein-Nishina effects on Synchrotron and Synchrotron self-Compton spectrum
Authors:		Nakar, Ehud; Ando, Shin'ichiro; Sari, Re'em
Publication:		eprint arXiv:0903.2557
Publication Date:		03/2009
Origin:		ARXIV
Keywords:		Astrophysics - High Energy Astrophysical Phenomena
Bibliographic Code:		2009arXiv0903.2557N

Abstract

We present analytic approximations to the optically thin synchrotron and synchrotron self-Compton (SSC) spectra when Klien-Nishina (KN) effects are important and pair production and external radiation fields can be neglected. This theory is useful for analytical treatment of radiation from astrophysical sources, such as gamma-ray bursts (GRBs), active galactic nuclei and pulsar wind nebula, where KN effects may be important. We consider a source with a continuous injection of relativistic electrons with a power-law energy distribution above some typical injection energy. We find that the synchrotron-SSC spectra can be described by a broken power-law, and provide analytical estimates for the break frequencies and power-law indices. In general, we show that the dependence of the KN cross-section on the energy of the upscattering electron results in a hardening of the energy distribution of fast cooling electrons and therefore in a hardening of the observed synchrotron spectrum. As a result, for example, the synchrotron spectrum of fast cooling electrons, below the typical injection energy, can be as hard as $F_\nu \propto \nu^0$, instead of the classical $\nu^{-1/2}$ when KN effects are neglected. Another example is that the synchrotron energy output can be dominated by electrons with energy above the typical injection energy. We solve self-consistently for the cooling frequency and find that the transition between synchrotron and SSC cooling can result in a discontinuous variations of the cooling frequency and the synchrotron and SSC spectra. We demonstrate the application of our results to theory by applying them to prompt and afterglow emission models of GRBs.

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