Joint anisotropy and source count constraints on the contribution of blazars to the diffuse gamma-ray background

TL;DR

This study constrains blazars' contribution to the gamma-ray background by jointly analyzing source counts, intensity, and anisotropy, revealing unresolved blazars account for less than 20% of the background at 1-10 GeV.

Contribution

It introduces a joint analysis method combining source count distribution and anisotropy measurements to constrain blazar contributions to the gamma-ray background.

Findings

Unresolved blazars contribute less than 20% of the gamma-ray background at 1-10 GeV.

Blazars account for the majority of the measured anisotropy in that energy band.

Some models of unresolved blazar populations are excluded by anisotropy measurements.

Abstract

We place new constraints on the contribution of blazars to the large-scale isotropic gamma-ray background (IGRB) by jointly analyzing the measured source count distribution (logN-logS) of blazars and the measured intensity and anisotropy of the IGRB. We find that these measurements point to a consistent scenario in which unresolved blazars make less than 20% of the IGRB intensity at 1-10 GeV while accounting for the majority of the measured anisotropy in that energy band. These results indicate that the remaining fraction of the IGRB intensity is made by a component with a low level of intrinsic anisotropy. We determine upper limits on the anisotropy from non-blazar sources, adopting the best-fit parameters of the measured source count distribution to calculate the unresolved blazar anisotropy. In addition, we show that the anisotropy measurement excludes some recently proposed models of the unresolved blazar population.