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

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.

7 pages, 4 figures. v2: new section (Sec.III) and 2 figures added. Expanded discussions in the other sections. Results and conclusions unchanged. New Section III is also a reply to the comment of Harding & Abazajian arXiv:1204.3870 on this work

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