The X-ray morphology of the lensing galaxy cluster Cl0024+17

We report the analysis of a very deep ROSAT HRI observation on one of the most interesting, distant lensing clus- ters, Cl0024+17. Using the X-ray surface brightness we analyse the cluster morphology and constrain the gas and gravitational mass of the cluster. We confirm the small core radius of the mass halo of 66 25 +38 h 1 50 kpc for this cluster inferred previ- ously from a detailed strong lensing analysis by Tyson et al. (1998) and Smail et al. (1997). Using estimated gas tempera- tures we find a cluster mass of about 3-14 10 14 h 1 50 M for a fiducial radius of 3h 1 50 Mpc. This mass is lower than the mass implied by the weak lensing result of Bonnet et al. (1994) and inconsistent with a virial analysis based on the high observed galaxy velocity dispersion. The lower gravitational mass found in the present study implies, however, a gas mass fraction of the cluster e.g. at 1h 1 50 Mpc radius of 17(11-28) h 1:5 50 % well consistent with the general observations in rich clusters. This favours a lower mass value for the relaxed part of Cl0024+17 which could still be embedded in a larger structure achieving a consistency with the weak lensing observations.