MAGIC Gamma-ray Observations of the Perseus Galaxy Cluster
  In order to detect the gamma-ray emission from cosmic ray (CR) interactions
with the intra-cluster medium, the ground-based imaging Cherenkov telescope
MAGIC conducted the deepest-to-date observational campaign targeting a galaxy
cluster at very high-energies (> 100 GeV) and observed the Perseus cluster for
a total of 85 hr during 2009-2011. The observations constrain the average
CR-to-thermal pressure ratio to be 1-2% and the maximum CR acceleration
efficiency at structure formation shocks to be <50%. Alternatively, this may
argue for non-negligible CR transport processes such as CR streaming and
diffusion into the outer cluster regions. Additionally, assuming that the
Perseus radio mini-halo is generated by secondaries created in hadronic CR
interactions, the central magnetic field is limited to be > 4-9 muG. This range
is well below the field strength inferred from Faraday rotation measurements
and, therefore, the hadronic model remains a plausible explanation of the
Perseus radio mini-halo. Following this successful campaign, MAGIC is
continuing collecting data on Perseus.
