Abstract
Observational features in the low energy γ-ray spectra of Seyfert galaxies are interpreted in terms of broad and blueshifted annihilation radiation. The possibility that this ‘line’ emission is the underlying source of the bump in the cosmic diffuse γ-ray background is investigated. The observational data available in the literature are then used to estimate the maximum temperature of the electron positron plasma and the average positron annihilation rate for Seyfert galaxies. The assumption that other active nuclei, namely radio galaxies and quasars, are powered by the same annihilation mechanism is used to set limits on their contribution to the cosmic diffuse γ-ray background.
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