The Extragalactic Background Light Absorption Feature in the Blazar Component of the Extragalactic Gamma-ray Background

TL;DR

This paper investigates the absorption feature caused by the extragalactic background light in the gamma-ray emission from blazars, showing how it can inform models of the EBL and blazar populations with upcoming observations.

Contribution

It models the EBL absorption feature in blazar gamma-ray spectra for various luminosity functions, highlighting its potential to differentiate EBL models and blazar populations.

Findings

Higher contributions of high-redshift blazars lead to more prominent absorption features.

Absorption features can distinguish between different EBL models.

Upcoming Fermi observations will enable tests of these models.

Abstract

High-energy photons from cosmological emitters suffer attenuation due to pair production interactions with the extragalactic background light (EBL). The collective emission of any high-energy emitting cosmological population will exhibit an absorption feature at the highest energies. We calculate this absorption feature in the collective emission of blazars for various models of the blazar gamma-ray luminosity function (GLF) and the EBL. We find that models of the blazar GLF that predict higher relative contributions of high-redshift blazars to the blazar collective spectrum result in emission that is more susceptible to attenuation by the EBL, and hence result in more prominent absorption features, allowing for better differentiation amongst EBL models. We thus demonstrate that observations of such an absorption feature will contain information regarding both the blazar GLF and the EBL, and we discuss tests for EBL models and the blazar GLF that will become possible with upcoming Fermi observations.