Two-Phased Intra-Cluster Medium in the Centaurus Cluster of Galaxies

ASCA and ROSAT data of the Centaurus cluster were analyzed. A central excess in the radial brightness profile is found in the hard energy band up to 10keV. This requires a deeper central potential than a King-type one. A double-beta brightness distribution gives a good account of the data. A deprojected energy spectrum within a spherical region of radius 30 kpc at the cluster center indicates that the ICM cannot be isothermal there. Simultaneous fitting of the three (PSPC, GIS, and SIS) energy spectra extracted from the central 3' region showed that a two-temperature model that has temperatures of 1.4keV and 4.4keV and a common metallicity of 1.0 solar with the Galactic absorption gives the best description to the spectra. A cooling-flow spectral model did not give satisfactory fit. A 3-dimensional cluster model incorporating the two-phase picture, the double-beta brightness distribution, and the central metallicity increase reproduced the overall ASCA and ROSAT data successfully. The derived spatial distribution of the dark matter deviates from a King-type profile exhibiting a central excess, which is consistent with the Navvaro-Frenk-White model. The iron is revealed to be more widely spread than stars, which may have been caused by energetic supernovae and the motion of the cD galaxy. Since the derived characteristics of the cool phase including the temperature, angular extent, gas mass, and metallicity, are on a smooth extension of those of inter-stellar medium (ISM) of elliptical galaxies, the cool phase can be regarded as the ISM associated with the cD galaxy. The cool-phase X-ray emission is presumably sustained by energies dissipated by infalling mass to the cD galaxy in the course of cluster evolution.Comment: accepted for publication in Ap

X-ray observations of the rich cluster CL 0939+4713 and discovery of the strongly variable source RXJ0943.0+4701

Recent X-ray observations of the rich galaxy cluster CL 0939+4713 (or Abell 851) at z = 0.41 with the ROSAT/HRI as well as with the ASCA/GIS and ASCA/SIS instruments are presented and analysed. With the high resolution imaging data (ROSAT/HRI) we confirm and extend the earlier impression that the cluster has a lot of substructure. Two maxima of the cluster emission are obvious in the images, each of them shows even some internal structure. One of the subclusters can be nicely modeled with an elliptical model. For the total luminosity of the cluster in the ROSAT band we obtain L_X_,_0_._1_-_2_._4_k_e_V 6.4_-_0_._3"+"0"."7 x 10"4"4 erg/s, for the bolometric luminosity L_X_,_b_o_l 1.6_-_0_._3"+"0"."5 x 10"4"5 erg/s. We perform spectral fits for the two ASCA instruments and for the ROSAT/PSPC simultaneously. The most reliable numbers for the temperature and metallicity for the intracluster gas are T 7.6_-_1_._6"+"2"."8 keV and m = 0.22_-_0_._2_2"+"0"."2"4 m_sun, respectively. We find a relatively small total mass, a small gas mass ratio and a small iron mass to light ratio. These numbers together with relatively low luminosity for such an optically rich cluster and the pronounced substructure confirm that CL 0939+4713 is a young cluster still far away from a virialised state. (orig.)44 refs.Available from TIB Hannover: RN 9303(432) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

RXTE observation of NGC 6240 A search for the obscured active nucleus

The wide-band energy spectrum of NGC 6240 over the range 0.5-200 keV is investigated using the RXTE and ASCA data. The RXTE data provide the spectrum beyond the ASCA range (0.5-10 keV) with significant detection of signals up to 20 keV and the upper limits above 20 keV. The spectrum above 10 keV is found to be very flat. A strong iron-K emission line discovered in the previous ASCA observation is also confirmed with the RXTE PCA. These results provide further evidence for the dominance of a reflection component, i.e. emission from cool material illuminated by an AGN. By fitting the spectra obtained with RXTE and ASCA simultaneously, we satisfactorily modeled the AGN spectrum with a Compton reflection component and probably a transmitted AGN component penetrating through a thick absorber. The X-ray luminosity of the AGN is estimated to be in the range 4 x 10"4"3 - 6 x 10"4"4 ergs/s in the range 2-10 keV, which categorizes NGC 6240 among the most luminous Seyfert nuclei. The ratio of the 2-10 keV X-ray luminosity to the infrared luminosity, L_X(2 - 10 keV)/L_I_R, is 0.01 - 0.1, which implies a quite substantial, if not dominant, contribution of AGN to the infrared luminosity. (orig.)SIGLEAvailable from TIB Hannover: RN 9303(489) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman