Robust implications on Dark Matter from the first FERMI sky gamma map

TL;DR

The paper addresses constraining DM annihilation and decay signals using the first-year FERMI all-sky gamma-ray map by deriving robust, model-independent bounds that depend weakly on the DM density profile. The authors compute DM-induced gamma fluxes from Final State Radiation and Inverse Compton scattering, and compare them to FERMI data without subtracting astrophysical backgrounds, using a global $3\sigma$ bound across sky regions. They find that, to explain the $e^{\pm}$ excesses, DM must primarily annihilate or decay into leptons (notably $\mu^+\mu^-$, $4\mu$, or $4e$) and, for annihilations, require an isothermal-like halo; hadronic channels and $\tau$-rich final states are disfavored. The results significantly constrain DM interpretations of the $e^{\pm}$ data and imply that any DM signal in the FERMI spectrum would constitute a detectable component, with future data likely to tighten the bounds or reveal a DM contribution.

Abstract

We derive robust model-independent bounds on DM annihilations and decays from the first year of FERMI gamma-ray observations of the whole sky. These bounds only have a mild dependence on the DM density profile and allow the following DM interpretations of the PAMELA and FERMI electron/positron excesses: primary channels mu+ mu-, mu+ mu-mu+mu- or e+ e- e+ e-. An isothermal-like density profile is needed for annihilating DM. In all such cases, FERMI gamma spectra must contain a significant DM component, that may be probed in the future.

Figures (8)

• Figure 1: Subdivision of the sky and example of a bound from each different region. In parenthesis, the same bound is computed neglecting both the diffusion of $e^\pm$ and the finite volume of the Milky Way diffusion halo.
• Figure 2: Left: Fermi data compared with an example of best-fit DM annihilation signal. Photons above $\approx100 \,{\rm GeV}$ can be still contaminated by hadrons. The dotted line shows Inverse Compton computed neglecting $e^\pm$ diffusion and the finite volume of the diffusion halo. Right: Fermi preliminary extra-galactic data FERMIdiffuse compared with an example of best-fit DM decay signal.
• Figure 3: Fermi full-sky bounds on Final State Radiation $\gamma$-rays, for the DM annihilation modes indicated along the curves.
• Figure 4: Fermi full-sky bounds on Inverse Compton $\gamma$-rays, for the DM annihilation modes indicated along the curves.
• Figure 5: Example of how the Fermi IC$\gamma$ bound on $\sigma v$ changes as function of the height $L$ of the diffusion volume for different DM profiles. We here assumed DM annihilations into $\mu^+\mu^-$ with $M=1.3\,{\rm TeV}$, but this plot would be almost the same for other DM models.