Constraints on Cosmic Rays, Magnetic Fields, and Dark Matter from Gamma-Ray Observations of the Coma Cluster of Galaxies with VERITAS and Fermi
Creators: name: Arlen, T.
name: Aune, T.
name: Beilicke, M.
name: Benbow, W.
name: Bouvier, A.
name: Buckley, J. H.
name: Bugaev, V.
name: Byrum, K.
name: Cannon, A.
name: Cesarini, A.
name: Ciupik, L.
name: Collins-Hughes, E.
name: Connolly, M. P.
name: Cui, W.
name: Dickherber, R.
name: Dumm, J.
name: Falcone, A.
name: Federici, S.
name: Feng, Q.
name: Finley, J. P.
name: Finnegan, G.
name: Fortson, L.
name: Furniss, A.
name: Galante, N.
name: Gall, D.
name: Godambe, S.
name: Griffin, S.
name: Grube, J.
name: Gyuk, G.
name: Holder, J.
name: Huan, H.
name: Hughes, G.
name: Humensky, T. B.
name: Imran, A.
name: Kaaret, P.
name: Karlsson, N.
name: Kertzman, M.
name: Khassen, Y.
name: Kieda, D.
name: Krawczynski, H.
name: Krennrich, F.
name: Lee, K.
name: Madhavan, A. S
name: Maier, G.
name: Majumdar, P.
name: McArthur, S.
name: McCann, A.
name: Moriarty, P.
name: Mukherjee, R.
name: Nelson, T.
name: de Bhróithe, A. O'Faoláin
name: Ong, R. A.
name: Orr, M.
name: Otte, A. N.
name: Park, N.
name: Perkins, J. S.
name: Pohl, M.
name: Prokoph, H.
name: Quinn, J.
name: Ragan, K.
name: Reyes, L. C.
name: Reynolds, P. T.
name: Roache, E.
name: Ruppel, J.
name: Saxon, D. B.
name: Schroedter, M.
name: Sembroski, G. H.
name: Skole, C.
name: Smith, A. W.
name: Telezhinsky, I.
name: Tešić, G.
name: Theiling, M.
name: Thibadeau, S.
name: Tsurusaki, K.
name: Varlotta, A.
name: Vivier, M.
name: Wakely, S. P.
name: Ward, J. E.
name: Weinstein, A.
name: Welsing, R.
name: Williams, D. A.
name: Zitzer, B.
name: Pfrommer, C.
name: Pinzke, A.
Publisher: name: arXiv
Year: 2012
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: Observations of radio halos and relics in galaxy clusters indicate efficient electron acceleration. Protons should likewise be accelerated, suggesting that clusters may also be sources of very high-energy (VHE; E&gt;100 GeV) gamma-ray emission. We report here on VHE gamma-ray observations of the Coma galaxy cluster with the VERITAS array of imaging Cherenkov telescopes, with complementing Fermi-LAT observations at GeV energies. No significant gamma-ray emission from the Coma cluster was detected. Integral flux upper limits at the 99% confidence level were measured to be on the order of (2-5)*10^-8\ ph. m^-2 s^-1 (VERITAS, &gt;220 GeV} and ~2*10^-6 ph. m^-2 s^-1 (Fermi, 1-3 GeV), respectively. We use the gamma-ray upper limits to constrain CRs and magnetic fields in Coma. Using an analytical approach, the CR-to-thermal pressure ratio is constrained to be &lt; 16% from VERITAS data and &lt; 1.7% from Fermi data (averaged within the virial radius). These upper limits are starting to constrain the CR physics in self-consistent cosmological cluster simulations and cap the maximum CR acceleration efficiency at structure formation shocks to be &lt;50%. Assuming that the radio-emitting electrons of the Coma halo result from hadronic CR interactions, the observations imply a lower limit on the central magnetic field in Coma of (2 - 5.5) muG, depending on the radial magnetic-field profile and on the gamma-ray spectral index. Since these values are below those inferred by Faraday rotation measurements in Coma (for most of the parameter space), this {renders} the hadronic model a very plausible explanation of the Coma radio halo. Finally, since galaxy clusters are dark-matter (DM) dominated, the VERITAS upper limits have been used to place constraints on the thermally-averaged product of the total self-annihilation cross section and the relative velocity of the DM particles, . (abr.)
description: ApJ in press