  Chandra observations of lensing galaxy clusters have now provided accurate
dark matter profiles for several objects in which the intracluster medium is
likely to be in hydrostatic equilibrium. We discuss Chandra observations of the
mass profile of one such cluster, EMSS1358+6245. We find no evidence for
flattening of the mass density profile at radii greater than 50/h_50 kpc . This
result, and similar findings from Chandra observations of other clusters,
appear to rule out models in of dark matter self-interaction proposed to
explain the flat cores of low-surface brightness galaxies.

Astrophysics