2003ApJ...588L..73D

We measure the average gravitational shear profile of six massive clusters (M_vir∼10¹⁵ M_☉) at z=0.3 out to a radius of ∼2 h^–1 Mpc. The measurements are fitted to a generalized Navarro-Frenk-White-like halo model ρ(r) with an arbitrary r⟶0 slope, α. The data are well fitted by such a model with a central cusp with α∼0.9-1.6 (68% confidence interval). For the standard Navarro-Frenk-White case α=1.0, we find a concentration parameter c_virthat 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 σ upper limit for the core radius corresponds to a limit σ_*≤0.1 cm²/g on the elastic collision cross section in a self-interacting dark matter model.