Fermi Bubbles under Dark Matter Scrutiny Part I: Astrophysical Analysis

The quest for Dark Matter signals in the gamma-ray sky is one of the most intriguing and exciting challenges in astrophysics. In this paper we perform the analysis of the energy spectrum of the Fermi bubbles at different latitudes, making use of the gamma-ray data collected by the Fermi Large Area Telescope. By exploring various setups for the full-sky analysis we achieve stable results in all the analyzed latitudes. At high latitude, |b | = 20◦−50◦, the Fermi bubbles energy spectrum can be reproduced by gamma-ray photons generated by inverse Compton scattering processes, assuming the existence of a population of high-energy electrons. At low latitude, |b | = 10 ◦ − 20◦, the presence of a bump at Eγ ∼ 1 − 4 GeV, reveals the existence of an extra component compatible with Dark Matter annihilation. Our best-fit candidate corresponds to annihilation into bb with mass MDM = 61.8 +6.9 −4.9 GeV and cross section 〈σv 〉 = 3.30+0.69−0.49 × 10−26 cm3s−1. In addition, using the energy spectrum of the Fermi bubbles, we derive new conservative but stringent upper limits on the Dark Matter annihilation cross section