Isotropic X-ray bound on Primordial Black Hole Dark Matter

Understand

We revisit the constraints on evaporating primordial black holes (PBHs) from the isotropic X-ray and soft gamma-ray background in the mass range $10^{16}-10^{18}$ g.

• We find that they are stronger than usually inferred due to two neglected effects: i) The contribution of the annihilation radiation due to positrons emitted in the evaporation process.
• ii) The high-latitude, Galactic contribution to the measured isotropic flux.
• We study the dependence of the bounds from the datasets used, the positron annihilation conditions, and the inclusion of the astrophysical background.