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Title: EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources

Abstract

The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ -ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ -rays with the extragalactic background light (EBL) compared to the expectation from current knowledge of the density and cosmological evolution of the EBL. One of the suggested solutions to this problem involves the inhomogeneity of the EBL. In this paper, we study the effects of such inhomogeneity on the energy density of the EBL (which then also becomes anisotropic) and the resulting γγ 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 γγ opacity, for any realistic void size, is only of the order of ≲1% and much smaller than expected from a simple linear scaling of the γγ opacity with the line-of-sight galaxy underdensity due to a cosmic void.

Authors:
;  [1]
  1. Centre for Space Research, North-West University, Potchefstroom 2520 (South Africa)
Publication Date:
OSTI Identifier:
22663898
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANISOTROPY; COMPARATIVE EVALUATIONS; COSMIC GAMMA SOURCES; COSMOLOGY; DENSITY; ENERGY DENSITY; EVOLUTION; GALAXIES; GAMMA RADIATION; GAMMA SPECTRA; GEV RANGE; INTERACTIONS; OPACITY; REDUCTION; UNIVERSE; VISIBLE RADIATION

Citation Formats

Abdalla, Hassan, and Böttcher, Markus. EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/237.
Abdalla, Hassan, & Böttcher, Markus. EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources. United States. doi:10.3847/1538-4357/835/2/237.
Abdalla, Hassan, and Böttcher, Markus. Wed . "EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources". United States. doi:10.3847/1538-4357/835/2/237.
@article{osti_22663898,
title = {EBL Inhomogeneity and Hard-Spectrum Gamma-Ray Sources},
author = {Abdalla, Hassan and Böttcher, Markus},
abstractNote = {The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ -ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ -rays with the extragalactic background light (EBL) compared to the expectation from current knowledge of the density and cosmological evolution of the EBL. One of the suggested solutions to this problem involves the inhomogeneity of the EBL. In this paper, we study the effects of such inhomogeneity on the energy density of the EBL (which then also becomes anisotropic) and the resulting γγ 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 γγ opacity, for any realistic void size, is only of the order of ≲1% and much smaller than expected from a simple linear scaling of the γγ opacity with the line-of-sight galaxy underdensity due to a cosmic void.},
doi = {10.3847/1538-4357/835/2/237},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}