Cosmological Constraints from the Clustering Properties of the X-Ray   Brightest Abell-type Cluster Sample
  We present an analysis of the 2-point correlation function, of the X-ray Brightest Abell-type Cluster sample (XBACs; Ebeling et al. 1998) and of the cosmological constraints that it provides. If \xi(r) is modelled as a power-law, we find r_0=26.0 +/- 4.5 Mpc/h and \gamma=2.0 +/-0.4, with errors corresponding to 2\sigma uncertainties. Only a marginal increase of the correlation amplitude is found as the flux limit is increased from 5x10^{-12} cgs to 12x10^{-12} cgs, thus indicating a weak dependence of the correlation amplitude on the cluster X-ray luminosity. Furthermore, we present a method to predict correlation functions for flux-limited X-ray cluster samples from cosmological models. The method is based on the analytical recipe by Mo & White (1996) and on an empirical approach to convert cluster fluxes into masses. We use a maximum-likelihood method to place constraints on the model parameter space. We find that the shape parameter of the power spectrum lies in the 2\sigma range 0.05<\Gamma<0.20. As for the amplitude of the power-spectrum, we find \sigma_8 in the range 0.4-0.8 for \Omega_0=1 and 0.8-2.0 for \Omega_0=0.3. This result is in agreement with, although less constraining than, results based on the local cluster abundance. 
S. Borgani (INFN, Perugia, Italy), M. Plionis (National Observatory,   Athens, Greece), E. Kolokotronis (National Observator...