On Dark Matter Explanations of the Gamma-Ray Excesses from the Galactic Center and M31

TL;DR

This paper investigates gamma-ray excesses from the Galactic center and M31, proposing dark matter annihilation as a common origin and fitting models to the observed spectra.

Contribution

It demonstrates that the gamma-ray excesses in both regions are consistent with dark matter annihilation when considering J-factors and identifies best-fit parameters for various annihilation modes.

Findings

Gamma-ray excesses in GC and M31 are compatible with dark matter origin.

Good spectral fits achieved for two-body and four-body annihilation modes.

Dark matter models can explain the observed gamma-ray signals.

Abstract

The presence of an excess 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 mis-modeling 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 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.