Constraints on the cosmic ray cluster physics from a very deep observation of the Perseus cluster with MAGIC

TL;DR

This study used deep gamma-ray observations of the Perseus galaxy cluster with MAGIC telescopes to set new constraints on cosmic-ray physics, including their pressure, acceleration efficiency, and magnetic fields, despite no direct detection.

Contribution

First deep gamma-ray observation of Perseus with MAGIC providing stringent limits on cosmic-ray properties in galaxy clusters.

Findings

No detection of large-scale gamma-ray emission from Perseus.

Set upper limits on cosmic-ray pressure and acceleration efficiency.

Constrained the magnetic field strength in the cluster core.

Abstract

Galaxy clusters are the largest and most massive gravitationally bound structures known in the Universe. Cosmic-Ray (CR) hadrons accelerated at structure formation shocks and injected by galaxies, are confined in galaxy clusters where they accumulate for cosmological times. The presence of diffuse synchrotron radio emission in several clusters proves the existence of high-energy electrons, and magnetic fields. However, a direct proof of CR proton acceleration is missing. The presence of CR protons can be probe through the diffuse gamma-ray emission induced by their hadronic interaction with the Intra-Cluster Medium (ICM). The Perseus cluster, a nearby cool-core cluster, has been identified to be among the best candidates to detect such emission. We present here the results of a very deep observation of the Perseus cluster with the MAGIC telescopes, accumulating about 250 hours of data from 2009 to 2014. No evidence of large-scale very-high-energy gamma-ray emission from CR-ICM interactions has been detected. The derived flux upper limits in the TeV regime allow us to put stringent constraints on the physics of cluster CRs, in particular on the CR-to-thermal pressure, the CR acceleration efficiency at formation shocks and the magnetic field of the central cluster region.