Can Observations of 511 keV Line from the M31 Galaxy Shed Light on the AGN Jet Composition?

Positron annihilation line at 511 keV is a known component of the gamma-ray diffuse emission. It believed to be produced in Galaxy, but there could possible extragalactic contribution as well. E.g., positrons can jets active galactic nuclei (AGN) and after that accumulate gradually annihilate hot gaseous halos around galaxies. In this work we test hypothesis application an individual object—the Andromeda galaxy (M31) which close has supermassive black hole its center, powered AGN before. We compute growth history M31, relate it evolution jet luminosity estimate positron content halo. calculate photon flux due should observed Earth find value $$10^{-4}$$ cm $${}^{-2}$$ s $${}^{-1}$$ . very observational limits ( $${<}10^{-4}$$ ) set by INTEGRAL/SPI assumption point source, so further observations would able constrain leptonic models propagation cosmic rays circumgalactic medium large spiral