The effects of EBL inhomogeneity on the gamma-gamma absorption of VHE gamma-rays
Abstract
Very High Energy Gamma Rays (VHE; more than 100 GeV) from Cosmological Gamma Ray
Sources such as blazars can be absorbed by the Extragalactic Background light (EBL), which
leads to a high-energy cut-off in blazar spectral energy distributions. However, recent observa-
tions of distant gamma ray sources suggest that the universe is more transparent to VHE gamma
rays than expected from our current knowledge of a homogeneous EBL. One of the possible so-
lutions is the hypothesis that a reduced EBL opacity results from inhomogeneities of the EBL
density in particular if the line of sight to a blazar is passing through large voids in intergalactic
space. We have evaluated the inhomogeneous and anisotropic EBL density and resulting gamma-
gamma opacity in such a case. We find that even a sizeable void
R
.
1
h
−
1
Gpc or many typical
voids
R
.
100
h
−
1
Mpc located along the line of sight to a distant blazar leads to a reduction
of the EBL opacity only around 15%. EBL inhomogeneities are not expected to reduce the EBL
gamma-gamma opacity significantly, and alternative solutions to the problem of hard VHE spectra
of blazars may be required
URI
http://hdl.handle.net/10394/26006https://pos.sissa.it/275/011/
https://pos.sissa.it/275/011/pdf