Absorption of Photons from Distant Gamma-Ray Sources

TL;DR

This paper investigates how high-energy gamma-ray photons from distant sources are absorbed by bremsstrahlung radiation in galaxy clusters, revealing a subtle but measurable effect in the 1-100 GeV energy range.

Contribution

It provides the first detailed calculation of gamma-ray absorption by galaxy cluster bremsstrahlung, highlighting its significance relative to other cosmic absorption effects.

Findings

Absorption effect occurs in the 1-100 GeV energy range.

Optical depth of the effect is approximately 10^{-5}.

Effect is third in magnitude after CMB and extragalactic background light absorption.

Abstract

Being the largest gravitationally bound structures in the Universe, galaxy clusters are huge reservoirs of photons generated by the bremsstrahlung of a hot cluster gas. We consider the absorption of high-energy photons from distant cosmological gamma-ray sources by the bremsstrahlung of galaxy clusters. The magnitude of this effect is the third in order of smallness after the effects of absorption by the cosmic microwave background and absorption by the extragalactic background light. Our calculations of the effect of absorption by the bremsstrahlung of galaxy clusters have shown that this effect manifests itself in the energy range 1--100 GeV and can be $\tau \sim 10^{-5}$.