Neutral atomic hydrogen absorption and the Galactic Center Excess

Abstract

An excess of gamma rays has been observed in the Galactic center region by Fermi-LAT. In order to characterise these gamma rays accurate estimates of the diffuse galactic background are needed. We improve the determination of the component of the diffuse galactic background caused by cosmic rays colliding with neutral atomic hydrogen (H ). We account for both line and continuum emission in the radiation transport. This allows the modelling of negative line intensity and traces gas both in emission and absorption. We find Fermi-LAT templates generated from such a model provide an improved fit in comparison to templates generated from previous models which do not account for the continuum component. But this does not change the conclusion that the unresolved population of millisecond pulsars model of the GCE provides a better fit than the self-annihilating dark matter model of the GCE.

ICRC 2021: Gamma-ray Direct Rapporteur

“…Several analyses looking at the galactic center (GC) including first results from DAMPE of the Fermi Bubbles [30] and GC lines [31], the GC as a high-energy particle accelerator [32], modeling neutral atomic Hydrogen to improve the GC fit [33], Galactic CO maps [34], Al-26 spectroscopy in the Galaxy [35], Cosmic-ray acceleration sites in the galaxy [36,37], and adaptive template fitting to understand the Fermi GC excess [38].…”