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2013MNRAS.429.2069D - Mon. Not. R. Astron. Soc., 429, 2069-2079 (2013/March-1)
A stacked analysis of brightest cluster galaxies observed with the Fermi large area telescope.
DUTSON K.L., WHITE R.J., EDGE A.C., HINTON J.A. and HOGAN M.T.
Abstract (from CDS):
For a >300 MeV selection, the distribution of detection significance across the sample is consistent with that across control samples for significances <3σ, but has a tail extending to higher values, including three >4σ signals which are not associated with previously identified γ-ray emission. Modelling of the data in these fields results in the detection of four non-2FGL Fermi sources, though none of these appear to be unambiguously associated with the BCG candidate. Only one is sufficiently close to be a plausible counterpart (RXC J0132.6-0804) and the remaining three appear to be background active galactic nuclei. A search at energies >3 GeV hints at emission from the BCG in A2055, which hosts a BL Lac object.
There is no evidence for a signal in the stacked data, and the upper limit derived on the γ-ray flux of an average radio-bright BCG in each band is at least an order of magnitude more constraining than that calculated for individual objects. F1GeV/F1.4GHz for an average BCG in the sample is <15, compared with ~120 for NGC 1275 in Perseus, which might indicate a special case for those objects detected at high energies. The tentative suggestion that point-like beamed emission from member galaxies comprise the dominant bright γ-ray sources in clusters implies searches for evidence of dark matter annihilation or large-scale merger shock signatures, for example, need to account for a significant level of contamination from within each cluster that is both highly stochastic and varies significantly over time.
Abstract Copyright: © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2012)
Journal keyword(s): radiation mechanisms: non-thermal - galaxies: active - galaxies: clusters: general - gamma-rays: galaxies: clusters - radio continuum: general
Simbad objects: 136
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