Clay, R.Stamatescu, V.Swaby, D.Thornton, G.Kiuchi, R.Mori, M.Bicknell, G.Edwards, P.Enomoto, R.Gunji, S.Hara, S.Hara, T.Hattori, T.Hayashi, S.Higashi, Y.Hirai, Y.Inoue, K.Itoh, C.Kabuki, S.Kajino, F.et al.2010-06-152010-06-152009The Astrophysical Journal: an international review of astronomy and astronomical physics, 2009; 704(1):240-2460004-637X1538-4357http://hdl.handle.net/2440/58858Because accretion and merger shocks in clusters of galaxies may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmic rays. A prediction was presented for gamma-ray emission from a cluster of galaxies at a detectable level with the current generation of imaging atmospheric Cherenkov telescopes. The gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We observed two clusters of galaxies, Abell 3667 and Abell 4038, searching for very high energy gamma-ray emission with the CANGAROO-III atmospheric Cherenkov telescope system in 2006. The analysis showed no significant excess around these clusters, yielding upper limits on the gamma-ray emission. From a comparison of the upper limit for the northwest radio relic region of Abell 3667 with a model prediction, we derive a lower limit for the magnetic field of the region of ~0.1 μG. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions using a model of gamma-ray emission from neutral pions produced in hadronic collisions of cosmic-ray protons with the intracluster medium. The derived upper limit of the cosmic-ray energy density within this framework is an order of magnitude higher than that of our Galaxyen© IOP Publishing 2009. Submitted to Cornell University’s online archive www.arXiv.org in 2009 by Ryuta Kiuchi.Post-print sourced from www.arxiv.org.High Energy Astrophysical Phenomena (astro-ph.HE)Cangaroo-III search for TeV gamma rays from two clusters of galaxiesJournal article002009395910.1088/0004-637X/704/1/2400002702195000202-s2.0-7044974687036647Clay, R. [0000-0002-9040-9648]