2009/08/23 by R. Kiuchi, M. Mori, G. V. Bicknell +47 · 18 citations
Physics and Astronomy · #Accretion (finance) #Active galactic nucleus #Astrophysics and Cosmic Phenomena #Cluster (spacecraft) #Cosmic ray #Dark Matter and Cosmic Phenomena #Galaxies: Formation, Evolution, Phenomena #Galaxy #Galaxy cluster #Galaxy groups and clusters #Gamma ray #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/704/1/240
published in The Astrophysical Journal 704(1), 240-246 (IOP Publishing) · 7 pages, 6 figures, Accepted in ApJ
arxiv created 2009/08/23 · openalex publication_date 2009/09/22 · arxiv updated 2015/05/14 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
Because 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 Galaxy.