A2163 - AN EXCEPTIONALLY HOT CLUSTER OF GALAXIES

We measured the X-ray spectrum of the distant galaxy cluster A2163 in the energy range 1-18 keV with the Ginga satellite. A combined analysis of these data with data previously obtained with the Einstein Observatory is presented. The mean temperature and X-ray luminosity we derive are exceptionally high compared to other clusters: kT = 12.9 keV, L(X) (2-10 keV) = 3.5 x 10(45) ergs s-1 for z = 0.15, as are the gas mass (6.7 x 10(14) M.) and binding mass (25 x 10(14) M.). The very existence of such a cluster can provide interesting constraints on the relative distribution of "visible" mass and dark matter, an important parameter in cold dark matter models for formation of structure in the universe.