Counting gamma rays in the directions of galaxy clusters

Abstract

Emission of AGNs and neutral pion decay - are the two most natural mechanisms, that could make a galaxy cluster be a source of gamma-rays in the GeV regime. We revisited this problem by using 52.5-month FERMI-LAT data above 10 GeV and stacking 55 clusters from the HIFLUGS sample of the X-ray brightest clusters. The choice of >10 GeV photons is optimal from the point of view of angular resolution, while the sample selection optimizes the chances of detecting signatures of the neutral pion decay, arising from hadronic interactions of relativistic protons with an intra-cluster medium, which scale with the X-ray flux. In the stacked data we detected a signal for the central 0.25 deg circle at the level of 4.3 sigma. An evidence for a spatial extent of the signal is marginal. A subsample of cool-core clusters has higher count rate 1.9+/-0.3 per cluster compared to the subsample of non-cool core clusters 1.3+/-0.2. Several independent arguments suggest that the contribution of AGNs to the observed signal is substantial if not dominant. No strong support for the large contribution of pion decay was found. In terms of a limit on the relativistic protons energy density, we got an upper limit of ~1.5% relative to the gas thermal energy density, provided that the spectrum of relativistic protons is hard (s=4.1 in dN/dp=p^-s). This estimate assumes that relativistic and thermal components are mixed. For softer spectra the limits are weaker.

13 pages, 6 figures, submitted to A&A on August, 6

References in corpus (18)

• The Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived From First-Year Fermi Large Area Telescope Data
• The Fermi Large Area Telescope On Orbit: Event Classification, Instrument Response Functions, and Calibration
• Compressible Turbulence in Galaxy Clusters: Physics and Stochastic Particle Re-acceleration
• Observations of extended radio emission in clusters
• Statistics of X-ray observables for the cooling-core and non-cooling core galaxy clusters
• CGRaBS: An All-Sky Survey of Gamma-Ray Blazar Candidates
• The First Fermi-LAT Catalog of Sources Above 10 GeV
• Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
• Giant Ringlike Radio Structures Around Galaxy Cluster Abell 3376
• Search for cosmic-ray induced gamma-ray emission in Galaxy Clusters
• Measuring the non-thermal pressure in early type galaxy atmospheres: A comparison of X-ray and optical potential profiles in M87 and NGC1399
• Gamma ray astrophysics: the EGRET results
• Probing the cosmic-ray content of galaxy clusters by stacking Fermi-LAT count maps
• The Anti-Coincidence Detector for the GLAST Large Area Telescope
• Fermi Gamma-ray Space Telescope: High-Energy Results from the First Year
• Nonthermal radiation mechanisms
• A Stacked Analysis of Brightest Cluster Galaxies Observed with the Fermi Large Area Telescope
• Non-thermal processes in the cluster of galaxies Abell 3376

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