Scrutinizing the Isotropic Gamma-Ray Background in Search of Dark Matter

TL;DR

This paper models the isotropic gamma-ray background considering astrophysical sources and dark matter, deriving constraints on dark matter properties and noting a potential excess flux consistent with galactic center observations.

Contribution

It introduces a comprehensive model combining astrophysical sources and dark matter annihilation to constrain dark matter properties using Fermi-LAT data.

Findings

Constraints on dark matter annihilation cross section are competitive with dwarf galaxy limits.

Potential small excess flux in the IGRB suggests possible dark matter or astrophysical origin.

Results align with gamma-ray excess observed at the galactic center.

Abstract

The isotropic gamma-ray background (IGRB), measured by the Fermi Large Area Telescope, is the result of several classes of extragalactic astrophysical sources. Those sources include blazars, start-forming galaxies and radio galaxies. Also, ultra-high-energy cosmic rays interacting with the infrared background, contribute to the isotropic background. Using information from Fermi's gamma-ray sources catalog and the results of dedicated studies of these classes of sources, from observations at the infrared and radio, we model their contribution to the IGRB. In addition to conventional astrophysical sources, dark matter may be a component of the IGRB. We combine our model of conventional astrophysical sources and of dark matter annihilation in distant galaxies, marginalizing over relevant uncertainties, to derive constraints on the dark matter annihilation cross section, from the measured IGRB. In calculating the contribution from dark matter we include the flux from extragalactic halos and their substructure and also the subdominant contribution from Milky Way's halo at high galactic latitudes. The resulting constraints are competitive with the strongest current constraints from the dwarf spheroidal galaxies. Under certain dark matter assumptions, we also find an indication for a small excess flux in the isotropic background. Our results are consistent with the gamma-ray excess at GeV energies toward the galactic center.