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arXiv 1210.8071astro-ph.HE
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超新星遗迹中来自宇宙射线的γ射线

Gamma Rays from Cosmic Rays in Supernova Remnants

C. D. Dermer, G. Powale

摘要:

背景:宇宙射线被认为是在超新星遗迹(SNR)的冲击加速,但缺乏确凿的证据。目的:来自地面伽马射线望远镜和费米伽马射线太空望远镜上的大面积望远镜的新数据被用来验证这一假设。一个简单的伽马射线生产效率的模型进行了比较,与测量的伽马射线光度的SNR,和GeV的TeV的流量比的SNR检查与SNR年龄的相关性。研究方法:超新星爆炸被模拟为一个不断膨胀的球形物质壳,它将周围的星际介质(ISM)扫起。壳层的累积动能为非热粒子加速提供了能量,当物质从ISM中被扫出时,SNR壳层减速。这些能量中的一部分被假定转化为宇宙射线电子或质子的能量。三种不同的粒子辐射过程-核π介子生产相互作用,非热电子韧致辐射,康普顿散射-被认为是。结果:比较了这三种方法的γ射线产生效率和信噪比。我们的研究结果表明,超新星遗迹在>~10^4年时伽马射线亮度变低,这与超新星遗迹加速宇宙射线的假设是一致的,即超新星遗迹将动能耗散为非热宇宙射线的效率约为10%。弱的证据,增加GeV TeV的流量比与SNR年龄。

英文摘要:

Context: Cosmic rays are thought to be accelerated at supernova remnant (SNR) shocks, but conclusive evidence is lacking. Aims: New data from ground-based gamma-ray telescopes and the Large Area Telescope on the Fermi Gamma-ray Space Telescope are used to test this hypothesis. A simple model for gamma-ray production efficiency is compared with measured gamma-ray luminosities of SNRs, and the GeV to TeV fluxes ratios of SNRs are examined for correlations with SNR ages. Methods: The supernova explosion is modeled as an expanding spherical shell of material that sweeps up matter from the surrounding interstellar medium (ISM). The accumulated kinetic energy of the shell, which provides the energy available for nonthermal particle acceleration, changes when matter is swept up from the ISM and the SNR shell decelerates. A fraction of this energy is assumed to be converted into the energy of cosmic-ray electrons or protons. Three different particle radiation processes---nuclear pion-production interactions, nonthermal electron bremsstrahlung, and Compton scattering---are considered. Results: The efficiencies for gamma-ray production by these three processes are compared with gamma-ray luminosities of SNRs. Our results suggest that SNRs become less gamma-ray luminous at >~ 10^4 yr, and are consistent with the hypothesis that supernova remnants accelerate cosmic rays with an efficiency of ~10% for the dissipation of kinetic energy into nonthermal cosmic rays. Weak evidence for an increasing GeV to TeV flux ratio with SNR age is found.

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