A Phantom Menace: On the Morphology of the Galactic Center Excess

Abstract

The characteristics of the Galactic Center Excess (GCE) emission observed in gamma-ray energies -- especially the morphology of the GCE -- remain a hotly debated subject. The manner in which the dominant diffuse gamma-ray background is modeled has been claimed to have a determining effect on the preferred morphology. In this work, we compare two distinct approaches to the galactic diffuse gamma-ray emission background: the first approach models this emission through templates calculated from a sequence of well-defined astrophysical assumptions, while the second approach divides surrogates for the background gamma-ray emission into cylindrical galactocentric rings with free independent normalizations. At the latitudes that we focus on, we find that the former approach works better, and that the overall best fit is obtained for an astrophysically motivated fit when the GCE follows the morphology expected of dark matter annihilation. Quantitatively, the improvement compared to the best ring-based fits is roughly 6500 in the chi^2 and roughly 4000 in the log of the Bayesian evidence.

10 pages (including the appendix), code available at https://github.com/samueldmcdermott/gcepy

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• Multi-Component Imaging of the Fermi Gamma-ray Sky in the Spatio-spectral Domain
• Towards resolving the Galactic center GeV excess with millisecond-pulsar-like sources using machine learning
• Applying Simulation-Based Inference to Spectral and Spatial Information from the Galactic Center Gamma-Ray Excess
• Observations of the Fermi bubbles and the Galactic center excess with the DArk Matter Particle Explorer
• Millisecond Pulsars in Globular Clusters and Implications for the Galactic Center Gamma-Ray Excess
• On the Energy Distribution of the Galactic Center Excess' Sources
• High Energy Emission from the Galactic Center