Models of the contribution of blazars to the anisotropy of the extragalactic diffuse gamma-ray background

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.
Comment: 17 pages, 5 figures; v2: updated KS-test comparison with the blazar redshift distribution and flux index distribution; removal of gamma1 < 0 parameter space, with small shift in best fit parameters; added references and discussion; matches published version in JCAP