The density profile of cluster-scale dark matter halos

We measure the average gravitational shear profile of six massive clusters (M-vir similar to 10(15) M-.)) at z = 0.3 out to a radius of similar to2 h(-1) Mpc. The measurements are fitted to a generalized Navarro-Frenk-White-like halo model rho(r) with an arbitrary r --> 0 slope, alpha. The data are well fitted by such a model with a central cusp with alpha similar to 0.9-1.6 (68% confidence interval). For the standard Navarro-Frenk-White case alpha = 1.0, we find a concentration parameter c(vir) that is consistent with recent predictions from high-resolution cold dark matter N-body simulations. Our data are also well fitted by an isothermal sphere model with a softened core. For this model, our 1 sigma upper limit for the core radius corresponds to a limit sigma(*) less than or equal to 0.1 cm(2) g(-1) on the elastic collision cross section in a self-interacting dark matter model.