TeV Gamma‐Ray Observations of the Perseus and Abell 2029 Galaxy Clusters

Galaxy clusters might be sources of TeV gamma rays emitted by high-energyprotons and electrons accelerated by large scale structure formation shocks,galactic winds, or active galactic nuclei. Furthermore, gamma rays may beproduced in dark matter particle annihilation processes at the cluster cores.We report on observations of the galaxy clusters Perseus and Abell 2029 usingthe 10 m Whipple Cherenkov telescope during the 2003-2004 and 2004-2005observing seasons. We apply a two-dimensional analysis technique to scrutinizethe clusters for TeV emission. In this paper we first determine flux upperlimits on TeV gamma-ray emission from point sources within the clusters.Second, we derive upper limits on the extended cluster emission. Wesubsequently compare the flux upper limits with EGRET upper limits at 100 MeVand theoretical models. Assuming that the gamma-ray surface brightness profilemimics that of the thermal X-ray emission and that the spectrum of clustercosmic rays extends all the way from thermal energies to multi-TeV energieswith a differential spectral index of -2.1, our results imply that the cosmicray proton energy density is less than 7.9% of the thermal energy density forthe Perseus cluster.Comment: Accepted for publication in the Astrophysical Journa