Compton observatory observations of clusters of galaxies and extragalactic radio sources

摘要

This task involved the investigation of the emission of clusters of galaxies, particularly those which contain extended radio emission, in the gamma-ray region of the spectrum. Observations were made of several clusters using the Compton Observatory EGRET instrument. For each cluster a measured flux or upper limit on the gamma-ray flux was obtained. In only one case, Abell 2199, was there a significant measured flux. This source is spatially confused with a known blazar in the field of view. The observation is consistent with all emission being from the blazar. Essentially, this program has led to an improvement of an order of magnitude on the upper limits for the gamma-ray luminosity of clusters of galaxies. This result has important implications in the studies of the metagalactic cosmic ray background, the composition of the unseen matter in clusters of galaxies and the mechanisms by which some clusters of galaxies generate synchrotron radio emission over megaparsec scales. Preliminary results of this analysis has been published in the Proceedings of the Second Compton Symposium (AIP Conference Proceedings 304, p669, 1993) and in conjunction with later observations at the High energy Astrophysics Division meeting of the AAS in November 1994. A final paper, funded separately, is being prepared for submission to the Astrophysical Journal.