Supermodel Analysis of the Hard X-Ray Excess in the Coma Cluster

The Supermodel provides an accurate description of the thermal contribution by the hot intracluster plasma which is crucial for the analysis of the hard excess. In this paper the thermal emissivity in the Coma cluster is derived starting from the intracluster gas temperature and density profiles obtained by the Supermodel analysis of X-ray observables: the XMM-Newton temperature profile and the Rosat brightness distribution. The Supermodel analysis of the BeppoSAX/PDS hard X-ray spectrum confirms our previous results, namely an excess at the c.l. of ~4.8sigma and a nonthermal flux of 1.30+-0.40x 10^-11 erg cm^-2 s^-1 in the energy range 20-80 keV. A recent joint XMM-Newton/Suzaku analysis reports an upper limit of ~6x10^-12 erg cm^-2 s^-1 in the energy range 20-80 keV for the nonthermal flux with an average gas temperature of 8.45+-0.06 keV, and an excess of nonthermal radiation at a confidence level above 4sigma, without including systematic effects, for an average XMM-Newton temperature of 8.2 keV in the Suzaku/HXD-PIN FOV, in agreement with our earlier PDS analysis. Here we present a further evidence of the compatibility between the Suzaku and BeppoSAX spectra, obtained by our Supermodel analysis of the PDS data, when the smaller size of the HXD-PIN FOV and the two different average temperatures derived by XMM-Newton and by the joint XMM-Newton/Suzaku analysis are taken into account. The consistency of the PDS and HXD-PIN spectra reaffirms the presence of a nonthermal component in the hard X-ray spectrum of the Coma cluster. The Supermodel analysis of the PDS data reports an excess at c.l. above 4sigma also for the higher average temperature of 8.45 keV thanks to the PDS FOV considerably greater than the HXD-PIN FOV.Comment: 18 pages, 7 figures, accepted for publication in Ap

Nonthermal emission from the radio relic of the galaxy cluster A2256

We aim to obtain a consistent description of non-thermal emissions from Abell 2256 and to give a prediction for a gamma-ray emission from this galaxy cluster. Assuming that a radio relic illuminates a localization of an ongoing merger, and that both radio and non-thermal part of hard X-ray emission are due to electron component of cosmic rays filling the relic, we derived from radio and hard X-ray properties of the relic in A2256 the magnetic field strength and number densities for relativistic electrons and protons. Due to the interpretation of the radio relic as a structure formed just where a shock front is, we discuss a gamma-ray emission at the cluster periphery. The estimated strength of the magnetic field in the relic is equal to 0.05 \muG, while the amplitude of the electron number density varies from 3 x 10^{-4} to 3 x 10^{-5} cm^{-3} (respectively for the relic thickness of 50 to 500 kpc). We got a substantial degree of non-equipartition between cosmic rays and magnetic field in the relic region, where the CR pressure is approaching that of thermal gas. Our prediction for LOFAR is a synchrotron flux from the relic region of the order of \sim 6 Jy at 60MHz and \sim 10 Jy at 30MHz. The lower limit of the gamma-ray flux from the relic region calculated for a hadronic channel is of the order of 10^{-12} erg cm^{-2}.Comment: 6 pages, 1 figure, Accepted for publication in A

Is there a hard tail in the Coma Cluster X-ray spectrum?

We report results from a re-analysis of the BeppoSAX observation of Coma and from the analysis of a second, yet unpublished observation of the same object. From our re-analysis of the first observation we find that the statistical evidence for a hard tail is about 2 sigma. From the analysis of the second observation which, thanks to the lower background and the longer exposure time, is characterized by a larger signal to noise we find no evidence for a hard tail. From the upper limit on the flux of the hard tail, using the standard Inverse Compton formulae, we derive a lower limit for the magnetic of about 0.2-0.4 microGauss consistent with Faraday rotation measurements.Comment: 4 pages, 2 figures, to appear in A&A Letter

Development of Hydrodynamic Instability in the Intergalactic Medium of the Merging Cluster of Galaxies A3667

A3667, a spectacular merger cluster, was observed by Chandra twice. In this paper we review the main results of the analysis of these observations. In particular we show evidence for the presence in the cluster of a 300 kpc Kelvin-Helmholtz hydrodynamic instability. We discuss the development of such instability and the structure of the intracluster magnetic filed in light of a self-consistent cluster dynamical model.Comment: 7 pages, color figures. To appear in Proc. "New Visions of the X-ray Universe in the XMM-Newton and Chandra Era", ESTEC, The Netherlands (Nov 2001), Eds. F.Janse

The giant radio halo in Abell 2163

New radio data is presented for the rich cluster Abell 2163. The cluster radio emission is characterized by the presence of a radio halo, which is one of the most powerful and extended halos known so far. In the NE peripheral cluster region, we also detect diffuse elongated emission, which we classify as a cluster relic. The cluster A2163 is very hot and luminous in X-ray. Its central region is probably in a highly non relaxed state, suggesting that this cluster is likely to be a recent merger. The existence of a radio halo in this cluster confirms that halos are associated with hot massive clusters, and confirms the connection between radio halos and cluster merger processes. The comparison between the radio emission of the halo and the cluster X-ray emission shows a close structural similarity. A power law correlation is found between the radio and X-ray brightness, with index = 0.64. We also report the upper limit to the hard X-ray emission, obtained from a BeppoSAX observation. We discuss the implications of our results.Comment: 7 pages, 8 figures (5 in ps and 3 in gif), Accepted for publication in Astron. Astrop

XMM-Newton observation of the cluster ZW 1305.4+2941 in the field SA 57

We report the details of an XMM observation of the cluster of galaxies ZW 1305.4+2941 at the intermediate redshift of z=0.241, increasing the small number of interesting X-ray constraints on properties of ~3 keV systems above z=0.1. Based on the 45 ks XMM observation, we find that within a radius of 228 kpc the cluster has an unabsorbed X-ray flux of 2.07 +/- 0.06 x 10^{-13} erg/cm^2/s, a temperature of kT = 3.17 +/-0.19 keV, in good agreement with the previous ROSAT determination, and an abundance of 0.93 (+0.24,-0.29} solar. Within r_500 = 723 +/- 6 kpc the rest-frame bolometric X-ray luminosity is L_X (r_500)= 1.25 +/- 0.16 x 10^{44} erg/s. The cluster obeys the scaling relations for L_X, T and the velocity dispersion derived at intermediate redshift for kT < 4 keV, for which we provide new fits for all literature objects. The mass derived from an isothermal NFW model fit is, M_vir = 2.77 +/- 0.21 x 10^{14} solar masses, with a concentration parameter, c = 7.9 +/- 0.5.Comment: 9 pages, 7 colour figures, accepted for publication in ApJ. Corrected typo on the fraction of blue galaxie

INTEGRAL discovery of non-thermal hard X-ray emission from the Ophiuchus cluster

We present the results of deep observations of the Ophiuchus cluster of galaxies with INTEGRAL in the 3-80 keV band. We analyse 3 Ms of INTEGRAL data on the Ophiuchus cluster with the IBIS/ISGRI hard X-ray imager and the JEM-X X-ray monitor. In the X-ray band using JEM-X, we show that the source is extended, and that the morphology is compatible with the results found by previous missions. Above 20 keV, we show that the size of the source is slightly larger than the PSF of the instrument, and is consistent with the soft X-ray morphology found with JEM-X and ASCA. Thanks to the constraints on the temperature provided by JEM-X, we show that the spectrum of the cluster is not well fitted by a single-temperature thermal Bremsstrahlung model, and that another spectral component is needed to explain the high energy data. We detect the high energy tail with a higher detection significance (6.4 sigma) than the BeppoSAX claim (2 sigma). Because of the imaging capabilities of JEM-X and ISGRI, we are able to exclude the possibility that the excess emission comes from very hot regions or absorbed AGN, which proves that the excess emission is indeed of non-thermal origin. Using the available radio data together with the non-thermal hard X-ray flux, we estimate a magnetic field B ~ 0.1-0.2 mu G.Comment: 8 pages, 9 figures, accepted by A&