Francesca Calore, Mattia Di Mauro, Fiorenza Donato
The nature of the Isotropic $\gamma$-ray Background (IGRB) measured by the Large Area Telescope (LAT) on the Fermi $\gamma$-ray space Telescope ({\it Fermi}) remains partially unexplained. Non-negligible contributions may originate from extragalactic populations of unresolved sources such as blazars or star-forming galaxies, or galactic milli-second pulsars. A recent prediction of the diffuse $\gamma$-ray emission from Active Galactic Nuclei (AGN) with a large viewing angle with respect to the line-of-sight (l.o.s.), has demonstrated that this faint but numerous population may explain from 10% up to the total of the IGRB intensity, depending on various astrophysical uncertainties. One more exotic contribution to the IGRB invokes the pair annihilation of dark matter (DM) weakly interacting massive particles (WIMP) into $\gamma$-rays. We evaluate the room left to galactic DM at high latitudes ($>10^\circ$), by taking into account the new result on the misaligned AGN (MAGN) contribution to the IGRB, together with the other significant galactic and extragalactic components. The DM signal is computed adding the Inverse Compton scattered photons to the prompt emission. Varying the level of MAGN diffuse emission within its theoretical uncertainties, we set stringent limits on the WIMPs' velocity averaged annihilation cross section \sigmav into $\gamma$-rays. Were the MAGN contribute about 60%-65% of the predicted maximal flux, the constraints on \sigmav would be set below the thermal decoupling cross section expected for a generic WIMP DM candidate, depending on the mass of the DM particlee and on the annihilation channel.
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http://arxiv.org/abs/1303.3284
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