Anisotropies in the diffuse gamma-ray background from dark matter with Fermi LAT: a closer look

Abstract

We perform a detailed study of the sensitivity to the anisotropies related to Dark Matter (DM) annihilation in the Isotropic Gamma-Ray Background (IGRB) as measured by the Fermi Large Area Telescope (Fermi-LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi-LAT. We consider DM anisotropies of extra-galactic origin and of Galactic origin (which can be generated through annihilation in the Milky Way sub-structures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 years of observation Fermi is sensitive to a DM contribution at the level of the thermal-relic cross section depending on the DM mass and annihilation mode. The anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle. (abridged)