X-RAY-PROPERTIES OF THE DISTANT CLUSTER CL0016+16

We present X-ray data on the distant cluster C10016 + 16 (z=0.5455) fr om ROSAT PSPC and HRI observations and use them to study the physics o f the intracluster medium (ICM) and the dynamical state of the cluster . The surface brightness distribution is described not only by a spher ically symmetric model but also by a two-dimensional beta-model fit. S ubtracting an elliptical model cluster as defined by the best-fitting parameters of the two-dimensional model we find significant residuals, indicating an additional, extended X-ray source within the cluster. T his source, likely to be a merging subcomponent of the cluster, agrees well with a peak in the weak-lensing-mass map of Small et al. In the course of this analysis we present a new approach for quantifying the significance of substructure in cluster X-ray images dominated by Pois son noise and smoothed with a Gauss filter. We determine the radial ma ss profile integrated out to a radius of 3 Mpc and find values of simi lar to 1.4-3.3 x 10(15) M-. for the gravitational mass of the cluster and similar to 4.5 x 10(14) M-. for the gas mass, yielding a gas-to-to tal mass ratio of 14-32 per cent. There is no significant radial depen dence of the gas-to-total mass ratio in the cluster.