MAGIC Gamma-ray Observations of the Perseus Galaxy Cluster

TL;DR

This study used the MAGIC telescope to observe the Perseus galaxy cluster for 85 hours, setting constraints on cosmic ray pressure, acceleration efficiency, and magnetic fields, and supporting the hadronic origin of the radio mini-halo.

Contribution

First deep VHE gamma-ray observations of Perseus with MAGIC, providing new constraints on cosmic ray physics and magnetic fields in galaxy clusters.

Findings

CR-to-thermal pressure ratio constrained to 1-2%

Maximum CR acceleration efficiency <50%

Central magnetic field > 4-9 μG

Abstract

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.