Correlation between the Halo Concentration c and the Virial Mass Mvir Determined from X-Ray Clusters

Numerical simulations of structure formation have suggested that there exists a good correlation between the halo concentration c (or the characteristic density deltac) and the virial mass Mvir for any virialized dark halo described by the Navarro, Frenk, & White density profile. In this Letter, we present an observational determination of the c-Mvir (or deltac-Mvir) relation in the mass range of approximately 1014 M middle dot in circle