Dark matter explanations of the gamma-ray excesses from the Galactic Center and M31

Abstract

The presence of an excess $\ensuremath{\gamma}$-ray signal toward the Galactic Center (GC) has now been well established, and is known as the GC excess. Leading explanations for the signal include mismodeling of the Galactic diffuse emission along the line of sight, an unresolved population of millisecond pulsars, and/or the annihilation of dark matter (DM). Recently, evidence for another excess $\ensuremath{\gamma}$-ray signal has been reported toward the outer halo of M31. In this work we interpret the excess signals from both the GC and outer halo of M31 in the framework of DM annihilation, and show that the two spectra are consistent with a DM origin once $J$-factors are taken into account. We further compare the excesses to models of DM annihilation, and determine the corresponding best-fit parameters. We find good fits to the spectrum both in two body and four body annihilation modes.