Dark Matter and Pulsar Model Constraints from Galactic Center Fermi-LAT Gamma Ray Observations

TL;DR

This study reevaluates gamma-ray excess at the Galactic center, considering uncertainties, and finds that a population of millisecond pulsars or specific dark matter models can explain the observations.

Contribution

It provides a systematic analysis of the Galactic diffuse emission uncertainties and assesses the viability of dark matter and pulsar models for the gamma-ray excess.

Findings

MSP population can fit the GC gamma-ray excess.

Pure tau+ tau- dark matter channel is a poor fit.

Mixed dark matter channels with specific parameters fit the data.

Abstract

Employing Fermi-LAT gamma ray observations, several independent groups have found excess extended gamma ray emission at the Galactic center (GC). Both, annihilating dark matter (DM) or a population of $\sim 10^3$ unresolved millisecond pulsars (MSPs) are regarded as well motivated possible explanations. However, there is significant uncertainties in the diffuse galactic background at the GC. We have performed a revaluation of these two models for the extended gamma ray source at the GC by accounting for the systematic uncertainties of the Galactic diffuse emission model. We also marginalize over point source and diffuse background parameters in the region of interest. We show that the excess emission is significantly more extended than a point source. We find that the DM (or pulsars population) signal is larger than the systematic errors and therefore proceed to determine the sectors of parameter space that provide an acceptable fit to the data. We found that a population of order a 1000 MSPs with parameters consistent with the average spectral shape of Fermi-LAT measured MSPs was able to fit the GC excess emission. For DM, we found that a pure $\tau^+\tau^-$ annihilation channel is not a good fit to the data. But a mixture of $\tau^+\tau^-$ and $b\bar{b}$ with a $\left<\sigma v\right>$ of order the thermal relic value and a DM mass of around 20 to 60 GeV provides an adequate fit.