Fermi Bubbles under Dark Matter Scrutiny. Part I: Astrophysical Analysis

Abstract

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 \textit{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, $|b|=20^{\circ }-50^{\circ }$, the \textit{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, $|b|=10^{\circ }-20^{\circ }$, the presence of a bump at $E_{\gamma }\sim 1-4$ GeV, reveals the existence of an extra component compatible with Dark Matter annihilation. Our best-fit candidate corresponds to annihilation into $b\bar{b}$ with mass $M_{\mathrm{DM}}=61.8_{-4.9}^{+6.9}$ GeV and cross section $<\sigma v>=3.30_{-0.49}^{+0.69}\times 10^{-26}$ cm${}^3$s${}^{-1}$. In addition, using the energy spectrum of the \textit{Fermi bubbles}, we derive new conservative but stringent upper limits on the Dark Matter annihilation cross section.

Comments: 23 pages + 2 appendices, 19 figures; v2: minor changes, various comments added in all the sections