New X-ray bound on density of primordial black holes

We set a new upper limit on the abundance of primordial black holes (PBH) based on existing X-ray data. PBH interactions with interstellar medium should result in significant fluxes of X-ray photons, which would contribute to the observed number density of compact X-ray objects in galaxies. The data constrain PBH number density in the mass range from a few M-circle dot to 2 x 10(7) M-circle dot. PBH density needed to account for the origin of black holes detected by LIGO is marginally allowed.