Implications of Cosmological Gamma-Ray Absorption II. Modification of gamma-ray spectra

TL;DR

This paper examines how gamma-ray spectra from distant sources are affected by absorption due to pair production with the evolving metagalactic radiation field, highlighting the influence of star formation and UV escape fractions.

Contribution

It models gamma-ray attenuation considering star formation rate variations and UV escape fractions, and explores how gamma-ray observations can measure the metagalactic radiation field across redshifts.

Findings

Gamma-ray attenuation depends on star formation history and UV escape fraction.

The gamma-ray cutoff can be used to probe the metagalactic radiation field.

Attenuation effects are significant for high-redshift TeV blazars.

Abstract

Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three observed TeV-blazars (Mkn501, Mkn421, H1426+428) we study the effects of gamma-ray attenuation on their spectra in detail.