A simple formula for the thermal pair annihilation line emissivity

Roland Svensson, Stefan Larsson, Juri Poutanen

Published 1996-07-13Version 1

We introduce a simple and convenient fitting formula for the thermal annihilation line from pair plasmas in cosmic sources. The fitting formula is accurate to 0.04\% and is valid at all photon energies and temperatures of interest. The commonly used Gaussian line profile is not a good approximation for broader lines.