Positron-annihilation radiation from neutron stars

Matter accreted on the surfaces of neutron stars consists of energetic particles of a few tens to one or two hundred MeV per nucleon, depending on the neutron-star mass. In addition to heat, such particles produce nuclear reactions with the surface material. We propose that the recently observed 473 + 30 keV spectral feature from the galactic center is gravitationally redshifted positron-annihilation radiation produced at the surfaces of neutron stars. The principal observational tests of the model would be the detection of nuclear y-ray lines from the galactic center. Subject headings: galactic nuclei - gamma rays - neutron stars - nuclear reactions