A gamma-ray halo "glow" from primordial black hole evaporation

It is well known that there is an isotropic diffuse flux of gamma rays from the universe. Some of the flux might be attributed to the evaporation of primordial black holes (PBHs) in the universe. If the PBHs cluster strongly in galactic halos, a gamma-ray halo "glow'' would be expected. Recent observations by the EGRET detector aboard the Compton Gamma Ray Observatory seem to have detected this glow, as well as an anisotropy in the flux. We first show that this is unlikely to be due to WIMP annihilation; then we show how this might be related to a possible signal of PBH evaporation in very short time gamma-ray bursts. We predict a glow in the Galactic halo and measurable anistropy, as well as a glow from any part of the universe where dark matter is concentrated from PBH evaporation.