Disentangling the gamma-ray emission of NGC 1275 and that of the Perseus cluster

Abstract

Context. The Gamma-ray emission from galaxy clusters hosting active galaxies is a complex combination of diffuse and point-like emission features with different spectral and spatial properties. Aims. We discuss in details the case of the Perseus cluster containing the radio-galaxy NGC 1275 that has been recently detected as a bright gamma-ray source by the Fermi-LAT experiment, in order to disentangle the sources of emission. Methods. 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 extended 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 both archival multi-frequency data and the recent very high energy observations obtained by Fermi and MAGIC. Results. We find that: i) in all the viable models for the cluster gamma-ray emission, the emission detected recently by Fermi from the center of the Perseus cluster 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 NGC 1275 is in a low-emission state; iii) Fermi can have the possibility to resolve and detect the diffuse gamma-ray flux (predicted by the WR model) coming from the outer corona of the Perseus cluster atmosphere at distances r > ∼ 800 kpc. These results are consistent with the evidence that in the other frequency bands, the diffuse cluster emission dominates on the central galaxy one at low radio frequencies with ν < ∼ 1 GHz and at X-ray energies of order of E ∼ keV. Conclusions. Our results show that a simultaneous study of the various emission mechanisms that produce diffuse gamma-rays from galaxy clusters and the study of the emission mechanisms that produce gamma-rays from active galaxies residing in the cluster atmospheres is absolutely 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.

Very high energy gamma-ray emission of NGC 1275 and 3c382 and the possible activity nature of the Seyfert Galaxies

“…The results of fifteen-year observation of NGC 1275 at energies from 800 GeV to 40 TeV are presented. A CM model [18] of gamma-ray emission of the Perseus cluster atmosphere and NGC 1275 is considered to describe the spectral properties of NGC 1275 in whole energy range. The Fermi LAT data at high energies and very high energy data from SHALON observations are well fitted in this model with three components [18], in which the most energetic and smaller blob produces a SSC emission observed at gamma-ray energies from MeV to TeV (Fig.…”

“…A CM model [18] of gamma-ray emission of the Perseus cluster atmosphere and NGC 1275 is considered to describe the spectral properties of NGC 1275 in whole energy range. The Fermi LAT data at high energies and very high energy data from SHALON observations are well fitted in this model with three components [18], in which the most energetic and smaller blob produces a SSC emission observed at gamma-ray energies from MeV to TeV (Fig. 9, red curve), whereas leptonic and hadronic models [18] of diffuse gamma-ray emission from the Perseus cluster (Fig.…”

“…8 No other significant variations of the γ-quantum flux during the observations of NGC1275 were found during all the period of observations. [12] and upper limits: EGRET [16] , Whipple [17], Veritas [10] and models [18] …”

“…9), where the spectrum of NGC 1275 from SHALON 15 year observations is also shown. Lines on Figure 9 show the fit to the multi-frequency spectral energy distribution of NGC 1275 obtained in the CM model [18] with the composition of three Synchrotron Self-Compton (SSC) components, generated by three separated plasma blobs blasted away from the NGC 1275 nucleus.…”

Disentangling cosmic-ray and dark-matter inducedγ-rays in galaxy clusters

“…However, this signal, also detected by Fermi-LAT (Abdo et al 2009), is consistent with an emission from the giant elliptical galaxy NGC 1275 lying at its centre (Aleksić et al 2010(Aleksić et al , 2012. From the Fermi-LAT results, Colafrancesco et al (2010) argue that it should be possible to resolve and detect the diffuse γ-ray flux of astrophysical origin coming from the outer corona of the Perseus cluster. Even more recently, Han et al (2012) reported a detection for Virgo, Fornax, and Coma from an analysis of Fermi-LAT data.…”