EGRET Excess of Diffuse Galactic Gamma Rays as a Trace of the Dark Matter Halo

摘要

The diffuse Galactic gamma ray data, which were measured by the EGRET experiment, show a clear excess for energies above 1 GeV in comparison with the expectations from conventional Galactic models. The excess is seen with a similar energy spectrum in all sky directions, as expected for Dark Matter (DM) annihilation. The spectral shape of the excess is used to limit the WIMP mass to the 50–100 GeV range, while its directional dependence is used to determine a halo profile, which is consistent with a triaxial isothermal halo with additional substructure of Dark Matter in the disc. The latter is strongly correlated with the ring of stars around our galaxy at a distance of 14 kpc, thought to originate from the tidal disruption of a dwarf galaxy. It is shown that this ring of DM causes the mysterious change of slope in the rotation curve at R = 1.1R₀.