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Title: Search for cosmic-ray-induced gamma-ray emission in galaxy clusters

Current theories predict relativistic hadronic particle populations in clusters of galaxies in addition to the already observed relativistic leptons. In these scenarios hadronic interactions give rise to neutral pions which decay into γ rays that are potentially observable with the Large Area Telescope (LAT) on board the Fermi space telescope. We present a joint likelihood analysis searching for spatially extended γ-ray emission at the locations of 50 galaxy clusters in four years of Fermi-LAT data under the assumption of the universal cosmic-ray (CR) model proposed by Pinzke and Pfrommer. We find an excess at a significance of 2.7σ, which upon closer inspection, however, is correlated to individual excess emission toward three galaxy clusters: A400, A1367, and A3112. We discuss these cases in detail and conservatively attribute the emission to unmodeled background systems (for example, radio galaxies within the clusters).Through the combined analysis of 50 clusters, we exclude hadronic injection efficiencies in simple hadronic models above 21% and establish limits on the CR to thermal pressure ratio within the virial radius, R {sub 200}, to be below 1.25%-1.4% depending on the morphological classification. In addition, we derive new limits on the γ-ray flux from individual clusters in our sample.
Authors:
;  [1] ;  [2] ;  [3] ; ; ; ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ; ;  [9] ; ;  [10] ;  [11] ;  [12] ;  [13] ;  [14] more »; ; « less
  1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
  2. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
  3. Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States)
  4. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
  5. Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
  6. Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa I-56127 Pisa (Italy)
  7. Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d'Astrophysique, CEA Saclay, F-91191 Gif sur Yvette (France)
  8. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
  9. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
  10. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
  11. Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
  12. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
  13. Dipartimento di Fisica "M. Merlin" dell'Università e del Politecnico di Bari, I-70126 Bari (Italy)
  14. Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
Publication Date:
OSTI Identifier:
22356869
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 787; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLASSIFICATION; COSMIC RADIATION; EFFICIENCY; EMISSION; GALAXY CLUSTERS; GAMMA RADIATION; INSPECTION; INTERACTIONS; LEPTONS; PARTICLE DECAY; RADIO GALAXIES; RELATIVISTIC RANGE; SPACE; TELESCOPES