Fermi-LAT Observations of Clusters of Galaxies
Abstract
We report on the search for gamma-ray emission from clusters of galaxies using the first 11 months of Fermi-LAT survey mode observations. Clusters are expected to host significant populations of energetic cosmic rays accelerated in accretion and merger shocks during structure formation as well as by active galactic nuclei and supernovae. The strongest observational evidence for this population comes from the detection of diffuse radio emission from many clusters. The relativistic electrons responsible for this emission can also produce gamma-rays via bremsstrahlung or inverse Compton processes. In addition, gamma-ray emission is expected as the result of collisions of cosmic ray protons with non-relativistic protons in the intracluster medium producing neutral pions which decay to yield gamma-rays. However, previous observations, including gamma-ray upper limits from EGRET, give only weak constraints on the energy density of cosmic rays in clusters. No clusters have been detected in the first 11 months of Fermi-LAT observations, and we use the unique sensitivity of Fermi in the GeV energy range to investigate the implications for the non-thermal particle content of galaxy clusters.
- Publication:
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AAS/High Energy Astrophysics Division #11
- Pub Date:
- March 2010
- Bibcode:
- 2010HEAD...11.3105J