On the Energy Distribution of the Galactic Center Excess' Sources

TL;DR

This paper introduces a neural network-based method that combines spatial and spectral data to analyze the Galactic Center Excess, suggesting it is either truly diffuse or made of an extremely large number of dim sources, aligning with dark matter predictions.

Contribution

It presents a novel simulation-based inference approach incorporating spectral data, significantly refining the understanding of the GCE's source population compared to prior spatial-only analyses.

Findings

Energy data indicates sources are much dimmer than previously thought.

The excess is consistent with Poisson emission from dark matter.

If due to point sources, there are over 100,000 sources in the Galactic Center.

Abstract

The Galactic Center Excess (GCE) remains one of the defining mysteries uncovered by the Fermi $\gamma$-ray Space Telescope. Although it may yet herald the discovery of annihilating dark matter, weighing against that conclusion are analyses showing the spatial structure of the emission appears more consistent with a population of dim point sources. Technical limitations have restricted prior analyses to studying the point-source hypothesis purely spatially. All spectral information that could help disentangle the GCE from the complex and uncertain astrophysical emission was discarded. We demonstrate that a neural network-aided simulation-based inference approach can overcome such limitations and thereby confront the point source explanation of the GCE with spatial and spectral data. The addition is profound: energy information drives the putative point sources to be significantly dimmer, indicating either the GCE is truly diffuse in nature or made of an exceptionally large number of sources. Quantitatively, for our best fit background model, the excess is essentially consistent with Poisson emission as predicted by dark matter. If the excess is instead due to point sources, our median prediction is ${\cal O}(10^5)$ sources in the Galactic Center, or more than 35,000 sources at 90% confidence, both significantly larger than the hundreds of sources preferred by earlier point-source analyses of the GCE.