One-photon annihilation of Lorentzian positrons in the interstellar medium

Abstract

We investigate one-photon annihilation of Lorentzian positrons with bound atomic electrons in the interstellar medium. The K and higher shell contributions, using the effective nuclear charges, are included to evaluate the annihilation rate of Lorentzian positrons. The results show that the one-photon positron annihilation rate increases with increasing positron temperature (T) over bar (+) (=T+/ryd), and decreases with increasing spectral index (kappa) for both the K and higher shell electrons. In addition, we find that positron annihilation rates for K-shell electrons are much larger than for higher shell electrons. At the intermediate positron temperature (T) over bar (+) = 1, the K-shell electrons of Si and C atoms produce the largest annihilation rates when kappa = 2 and 6, respectively. However, at the high temperature (T) over bar (+) = 10, the K-shell electrons of Si and Mg atoms provide the largest annihilation rates for kappa = 2 and 6. Hence, the annihilation rate is quite sensitive to the Lorentzian character of the positron distribution.