Constraining the cosmic abundance of stellar remnants with multi-TeV γ-rays

If galactic halos contain stellar remnants, the infra-red flux from the remnant progenitors would contribute to the opacity of multi-TeV γ-rays. The multi-TeV γ-ray horizon is established to be at a redshift z > 0.034 by the observation of the blazar Mkn501 . By requiring that the optical depth due to γγ −→ ee be less than one for a source at z = 0.034 we limit the cosmological density of stellar remnants, Ωrm ≤ (2−4)×10 h 70 (h70 is the Hubble constant in units of 70 km sec −1 Mpc) and thus strongly constrain stellar remnants as a cosmologically significant source of dark matter. Subject headings: white dwarfs, neutron stars, diffuse radiation Department of Physics, The Ohio State University, Columbus, OH 43210 Department of Astronomy, The Ohio State University, Columbus, OH 43210 Department of Physics, University of Michigan, Ann Arbor, MI 48109 Visitor, Max Planck Institut für Physik, Föhringer Ring 6, München, Germany