Testing gamma-ray models of blazars in the extragalactic sky

TL;DR

This paper combines statistical analyses of gamma-ray counts and angular power spectrum data from Fermi-LAT to model the gamma-ray emission of unresolved blazars, extending understanding to fluxes below detection thresholds.

Contribution

It introduces a novel approach combining one-point statistics and angular power spectrum measurements to constrain blazar gamma-ray properties at very low flux levels.

Findings

Consistent gamma-ray luminosity functions for blazars from different methods.

Extended the flux range for blazar models by nearly two orders of magnitude.

Demonstrated the complementarity of statistical and angular power spectrum analyses.

Abstract

The global contribution of unresolved gamma-ray point sources to the extragalactic gamma-ray background has been recently measured down to gamma-ray fluxes lower than those reached with standard source detection techniques, and by employing the statistical properties of the observed gamma-ray counts. We investigate and exploit the complementarity of the information brought by the one-point statistics of photon counts (using more than 10 years of Fermi-LAT data) and by the recent measurement of the angular power spectrum of the unresolved gamma-ray background (based on 8 years of Fermi-LAT data). We determine, under the assumption that the source-count distribution of the brightest unresolved objects is dominated by blazars, their gamma-ray luminosity function and spectral energy distribution down to fluxes almost two orders of magnitude smaller than the threshold for detecting resolved sources. The different approaches provide consistent predictions for the gamma-ray luminosity function of blazars, and they show a significant complementarity.