X-ray properties of the distant cluster Cl0016+16

We present X-ray data on the distant cluster C10016 + 16 (z=0.5455) from ROSAT PSPC and HRI observations and use them to study the physics of the intracluster medium (ICM) and the dynamical state of the cluster. The surface brightness distribution is described not only by a spherically symmetric model but also by a two-dimensional beta-model fit. Subtracting 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. This 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 Poisson noise and smoothed with a Gauss filter. We determine the radial mass profile integrated out to a radius of 3 Mpc and find values of similar 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-total mass ratio of 14-32 per cent. There is no significant radial dependence of the gas-to-total mass ratio in the cluster.