We present X-ray data on the distant cluster Cl0016 + 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 twodimensional If-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 weaklensing-mass map of Smail et aI. 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.
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Neumann et al. (1997) studied this question.