Evidence for Unresolved Gamma-Ray Point Sources in the Inner Galaxy

TL;DR

This paper introduces a new statistical method to analyze gamma-ray data, revealing that unresolved point sources can explain the Galactic Center excess, challenging dark matter interpretations.

Contribution

The paper develops a non-Poissonian template fitting method to characterize unresolved gamma-ray point sources in the Inner Galaxy.

Findings

Unresolved point sources account for ~5-10% of the gamma-ray flux near the Galactic Center.

Unresolved sources fully explain the observed gamma-ray excess in the Inner Galaxy.

Resolved and unresolved sources together make up about 50% of the extragalactic gamma-ray background.

Abstract

We present a new method to characterize unresolved point sources (PSs), generalizing traditional template fits to account for non-Poissonian photon statistics. We apply this method to Fermi Large Area Telescope gamma-ray data to characterize PS populations at high latitudes and in the Inner Galaxy. We find that PSs (resolved and unresolved) account for ~50% of the total extragalactic gamma-ray background in the energy range ~1.9 to 11.9 GeV. Within 10$^\circ$ of the Galactic Center with $|b| \geq 2^\circ$, we find that ~5-10% of the flux can be accounted for by a population of unresolved PSs, distributed consistently with the observed ~GeV gamma-ray excess in this region. The excess is fully absorbed by such a population, in preference to dark-matter annihilation. The inferred source population is dominated by near-threshold sources, which may be detectable in future searches.