Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2010-06-11
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
14 pages, 14 figures, A&A in press
Scientific paper
(Abridged). The gamma-ray emission from galaxy clusters hosting active galaxies is a complex combination of diffuse and point-like emission with different spectral and spatial properties. We discuss the case of the Perseus cluster containing the radio-galaxy NGC 1275 that has been detected as a bright gamma-ray source by the Fermi-LAT experiment. We provide a detailed study of the gamma-ray emission coming from the core of Perseus by modeling the central AGN emission with a multiple plasma blob model, and the emission from the cluster atmosphere with both a Warming Ray (WR) model and Dark Matter (DM) neutralino annihilation models. We set constraints on both the central galaxy and cluster SED models by using multi-frequency data including the observations obtained by Fermi and MAGIC. We find that: i) in all the viable models for the cluster gamma-ray emission, the emission detected by Fermi from the Perseus core is dominated by the active galaxy NGC 1275, that is found in a high-emission state; ii) the diffuse gamma-ray emission of the cluster, in the WR model and in the DM models with the highest allowed normalization, could be detected by Fermi if the central emission from NGC1275 is in a low-emission state; iii) Fermi can have the possibility to resolve and detect the diffuse gamma-ray flux coming from the outer corona of the Perseus atmosphere at r> 800 kpc. Our results show that a simultaneous study of the various emission mechanisms that produce diffuse gamma-rays from galaxy clusters and those producing gamma-rays from active galaxies residing in the cluster atmospheres is crucial first to disentangle the spectral and spatial characteristics of the gamma-ray emission and secondly to assess the optimal observational strategy in the attempt to reveal the still elusive diffuse gamma-ray emission widely predicted for the atmospheres of large-scale structures.
Colafrancesco Sergio
Giommi Paolo
Marchegiani Paolo
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