Are mildly active galaxies sources of e± annihilation radiation?

Abstract

The Galactic Center has been established as a source of 511 keV line radiation resulting from electron-position annihilation. The Galactic Center is also the site of a compact, nonthermal radio source similar to the scaled-down version of those found in the nuclei of active galaxies and quasars. This suggests that there is a mildly active central engine at the Galactic Center, which is capable of producing the high output of positrons required to explain the strength of the 511 keV line. If this is the case, then one would expect other active galaxies to also contain positron sources in their nuclei. Because of possible escape routes for positrons, it was decided that a promising candidate for 511 keV line detection would be any active galaxy whose nonthermal radio activity is contained within the galaxy. Seven galaxies were chosen using this criteria. The HEAO-3 ..gamma.. Ray Spectrometer was operable from 20 September 1979 until June 1980, and none of these galaxies were detected in the 511 keV line. 19 references, 1 table.