GeV photon absorption in cosmologically evolving quasar environments

TL;DR

This paper investigates how gamma-ray absorption in quasars evolves with redshift, revealing that optical depths depend on cosmic evolution of accretion rates, affecting interpretations of gamma-ray spectra and background light estimates.

Contribution

It demonstrates the redshift dependence of gamma-ray absorption in quasars due to cosmological evolution of accretion rates, impacting gamma-ray horizon studies.

Findings

Detectable gamma-ray optical depths increase with redshift for evolving accretion rates.

Redshift dependence introduces ambiguities in spectral absorption interpretation.

Implications for extragalactic background light estimation methods.

Abstract

The question of a possible redshift-dependence of gamma-ray absorption due to gamma-gamma pair production of jet photons in the accretion disk and BLR radiation field in strong-line quasars is investigated. For this relevant aspects of cosmological black hole and quasar evolution are applied to the expected pair production opacity of GeV-photons in those sources. I demonstrate that for positively evolving and non-evolving accretion rates over cosmological time, detectable gamma-ray optical depths originating within the AGN system will show a redshift-dependence in the LAT energy range with larger opacity from sources at higher redshifts. This introduces ambiguities in the interpretation of spectral absorption features, and complicates approaches for estimating the evolution of the extragalactic background light by probing the gamma-ray horizon when using blazars whose external photon fields are involved in gamma-ray production.