BeppoSAX - ROSAT PSPC observations of the Shapley Supercluster: A3562

Abstract

We present a combined analysis of the BeppoSAX and ROSAT PSPC observation of the cluster of galaxies A3562, a massive member of the core of the Shapley Supercluster. With a complex and interacting structure composed from two groups of galaxies and A3558 to the West, the surface brightness of A3562 shows excess in the sectors to East and South when compared with an azimuthally averaged model of the emission. The emission tends to be flatter, and the distribution of the gas broader, along the merging axis and in opposition to the two groups. We present the first determination of the gradients of the gas temperature and metallicity for a cluster in the Shapley region at large distance from cluster center. From an analysis of the BeppoSAX data in annuli and sectors, we observe both the profiles to be flat within 8 arcmin (0.62 Mpc), with an emission-weighted values of kT = 5.1+-0.2 keV and Z = 0.39+-0.05 Zsolar. The value of the temperature is consistent with recent ASCA measurements and is significantly higher than previous estimates obtained from ROSAT and EXOSAT. We discuss the possible reasons of this disagreement. Between 8 and 20 arcmin, the plasma temperature declines to about 3.2 keV. When a polytropic profile is used to represent the gas temperature profile, the best fit polytropic index is 1.16+-0.03. These results imply a total mass within the virial radius of 3.9 (+-0.4) 10^14 h_50^-1 Msolar, between 40 and 80 per cent lower than the optical estimate, and a gas mass fraction of about 30 per cent.