沿VHE γ射线路径的EBL的详细建模
Detailed modelling of the EBL along VHE γ-ray paths
摘要：
河外背景光（EBL）与来自宇宙源的甚高能γ射线（VHE; E > 10 GeV）相互作用，改变了它们的γ射线谱。较硬的γ射线的较强吸收导致在高能尾部观测到的γ射线谱的陡化，这可以通过功率指数的增加来表示。这种效应提供了高能天体物理学和星系演化之间的联系。在这项工作中，我们开发了一个新的混合EBL模型，通过增强我们以前的分析模型与半解析星系表的信息。该模型允许我们研究单个γ射线路径通过（模拟）宇宙的γ射线不透明度，并评估沿每条路径的EBL强度的局部波动的影响。我们确认了局部EBL的一个数量级波动（基于来自50 $h^{-1}$球内模型星系分布的累积光）。然而，由于局部EBL对总EBL的总体贡献非常小，因此这些波动对VHE γ射线不透明度的影响并不显着。我们还研究了穿过γ射线源视线的星系对VHE谱的影响。我们发现恒星质量为M $ > 10^{11}$ M $_{\odot}$的星系对γ射线吸收有显著的影响。观测到的光谱指数的变化不太可能是由于单个星系靠近γ射线路径造成的，因为这是非常罕见的。
英文摘要：
Interactions between the extragalactic background light (EBL) and very high energy γ rays (VHE; E > 10 GeV) from cosmological sources alter their γ-ray spectrum. The stronger absorption of harder γ rays causes a steepening of the observed γ-ray spectrum at the high energy tail which can be expressed by an increase of the power index. The effect provides a link between high energy astrophysics and the evolution of galaxies. In this work we develop a new hybrid EBL model by augmenting our previous analytic model with information from semi-analytic galaxy catalogues. The model allows us to study the γ-ray opacities of individual γ-ray paths through the (simulated) universe and evaluate the effect of local fluctuations in the EBL intensity along each path. We confirm an order of magnitude fluctuations in the local EBL (based on the cumulative light from model galaxy distributions within spheres of 50 $h^{-1}$Mpc). However, the effect of these fluctuations on the VHE γ-ray opacity is insignificant due to the overall very small contribution of the local EBL to the total EBL. We also investigate the effect which a galaxy crossing the line of sight of the γ-ray source may have on the VHE spectrum. We find that galaxies with stellar masses of M$ > 10^{11}$ M$_{\odot}$ could have significant effect on the γ-ray absorption. It is unlikely that the observed variation in the spectral index is caused by the proximity of single galaxies to the γ-ray paths as these are extremely rare.
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