A Multi-Wavelength Analysis of Annihilating Dark Matter as the Origin of the Gamma-Ray Emission from M31

Abstract

[Abridged] Indirect detection of dark matter (DM) by multi-wavelength astronomical observations provides a promising avenue for probing the particle nature of DM. In the case of DM consisting of Weakly-Interacting Massive Particles (WIMPs), self-annihilation ultimately produces observable products including $e^{\pm}$ pairs and gamma rays. The gamma rays can be detected directly, while the $e^{\pm}$ pairs can be detected by radio emission from synchrotron radiation or X-rays and soft gamma rays from inverse Compton scattering. An intriguing region to search for astrophysical signs of DM is the Galactic center (GC) of the Milky Way, due in part to an observed excess of gamma-rays that could be DM. A recent observation by the Fermi-LAT collaboration of a similar excess in the central region of the Andromeda galaxy (M31) leads us to explore the possibility of a DM-induced signal there as well. We use the RX-DMFIT tool to perform a multi-frequency analysis of potential DM annihilation emissions in M31. We consider WIMP models consistent with the GC excess and calculate the expected emission across the electromagnetic spectrum in comparison with available observational data from M31. We find that the particle models that best fit the M31 excess favor lower masses than the GC excess. The best fitting models are for a $b\bar{b}$ final state with $M_{\chi}=11$ GeV and $\left<\sigma v\right>=2.6\times 10^{-26}$ cm$^3$s$^{-1}$, as well as an evenly mixed $b\bar{b}/\tau^+\tau^-$ final state with $M_{\chi}=5.8$ GeV and $\left<\sigma v\right>=2.03\times 10^{-26}$ cm$^3$s$^{-1}$. For conservative estimates of the diffusion and magnetic field models the expected radio emissions appear to be in tension with currently available data in the central region of M31, although this constraint has a fairly strong dependence on the values chosen for parameters describing the magnetic field strength and geometry.