Detailed modelling of the EBL along VHE γ-ray paths
arXiv:1808.06205 · doi:10.1093/mnras/sty2269
Abstract
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 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 M 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.
arXiv comment10 pages, 11 figures
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