Observation Of The Perseus Cluster Of Galaxies With The MAGIC Gamma-Ray Telescope

The Perseus galaxy cluster was observed by the MAGIC Cherenkov telescope for a total effective time of 24.4 hours during November and December 2008. No significant γ-ray excess was detected. The resulting upper limits on the γ-ray emission above 100 GeV are 4.63 and 6.55 × 10−12cm−2 s−1 for spectral indices of −1.5 and −2.2, respectively. The obtained limits constrain the emission produced by cosmic rays and dark matter annihilation. The results are compatible with cosmological cluster simulations for the cosmic ray induced γ-ray emission, constraining the relative cosmic ray pressure to < 3.5% for the cluster core region (< 7% when considering biasing effects of galaxy-sized substructures). Using simplified assumptions adopted in earlier work (constant cosmic ray-to-thermal pressure throughout the entire cluster and a power-law spectrum with an index of −2.1), we constrain the ratio of cosmic ray-to-thermal energy to ECR/Eth < 1.7%. The upper limit also translates to a level of γ-ray emission from possible annihilations of the cluster dark matter (the dominant mass component) that is consistent with boost factors of ∼ 10 for the typically expected dark matter annihilation induced emission. Our estimations indicate that the Perseus galaxy cluster is the most promising cluster where to look for cosmic ray induced γ-ray emission.