The Mass Function of an X-Ray Flux-Limited Sample of Galaxy Clusters

Using the brightest clusters in the ROSAT All-Sky Survey we compiled an X-ray flux-limited sample of galaxy clusters. The clusters have been reanalysed using ROSAT PSPC pointed observations if possible. The gravitational mass has been determined individually for each cluster in a homogeneous way assuming hydrostatic equilibrium. The mass function has been derived. We present the preliminary results and a comparison to previous determinations.