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The unexpectedly hard very-high-energy (VHE; $E > 100$ GeV) $gamma$-ray spectra of a few distant blazars have been interpreted as evidence for a reduction of the $gammagamma$ opacity of the Universe due to the interaction of VHE $gamma$-rays with the extragalactic background light (EBL) compared to the expectation from our current knowledge of the density and cosmological evolution of the EBL. One of the suggested solutions to this problem consisted of the inhomogeneity of the EBL. In this paper, we study the effects of such inhomogeneities on the energy density of the EBL (which then also becomes anisotropic) and the resulting $gammagamma$ opacity. Specifically, we investigate the effects of cosmic voids along the line of sight to a distant blazar. We find that the effect of such voids on the $gammagamma$ opacity, for any realistic void size, is only of the order of $lesssim 1$ % and much smaller than expected from a simple linear scaling of the $gammagamma$ opacity with the line-of-sight galaxy under-density due to a cosmic void.
Very high-energy gamma-rays (VHE, E>100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the universe to VHE gam
This letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very-high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to
When a magnetically-dominated super-fast magnetosonic GRB jet leaves the progenitor star the external pressure support may drop and the jet may enter the regime of ballistic expansion during which its magnetic acceleration becomes highly ineffective.
We estimate the galaxy density along lines of sight to hard extragalactic gamma-ray sources by correlating source positions on the sky with a void catalog based on the Sloan Digital Sky Survey (SDSS). Extragalactic gamma-ray sources that are detected