Models of the Contribution of Blazars to the Anisotropy of the Extragalactic Diffuse Gamma-ray Background

TL;DR

This study models blazars' contribution to the gamma-ray background anisotropy, finding they explain the anisotropy but only account for a small fraction of the total intensity, highlighting model limitations.

Contribution

It introduces a physical-evolution model with luminosity-dependent evolution and spectral energy distribution for blazars, improving upon previous simplified assumptions.

Findings

Blazars can explain the observed anisotropy of the DGRB.

Blazars contribute approximately 5.7% of the DGRB intensity above 1 GeV.

Models without unjustified assumptions better match observations.

Abstract

We study the relation between the measured anisotropies in the extragalactic diffuse gamma-ray background (DGRB) and the DGRB spectral intensity, and their potential origin from the unresolved blazar population. Using a physical-evolution model for blazars with a luminosity dependent evolution (LDDE) and an observationally-determined luminosity-dependent blazar spectral energy distribution (SED), we find that blazars can account for the observed anisotropy of the DGRB consistent with their observed source-count distribution, but are in turn constrained in contributing significantly to the observed DGRB intensity. For the best-fit LDDE model accounting for the DGRB anisotropy and source-count distribution, blazars only contribute 5.7^{+2.1}_{-1.0}% (68% CL) of the DGRB intensity above 1 GeV. Requiring a higher fraction of the DGRB intensity contribution by blazars overproduces the DGRB anisotropy, and therefore blazars in the LDDE+SED-sequence model cannot simultaneously account for the DGRB intensity as well as anisotropy. We discuss the limitations of LDDE models. However, these models do not require the many unjustified and observationally-inconsistent simplifying assumptions---including a single power law for all blazar spectra and a simple broken power-law model for their source-count distribution---that are present in much previous work.