Low-energy positrons and gamma photons in the Galaxy

The problem of low-energy positron production in the Galaxy and subsequent annihilation of these positrons into gamma rays have produced many different hypotheses on the sources. The high intensity of gamma-ray emission sets certain limitations on the properties of these sources. In this review, we provide estimations of the contribution of cosmic rays to the production of low-energy positrons responsible for the formation of the 511-keV annihilation line. Despite cosmic rays being unable to provide a sufficient positron production rate to explain the annihilation emission of the whole Galaxy, their contribution is not negligible.