Temperature and Dark Matter profiles of Galaxy Groups
  The Chandra and XMM data for a sample of 19 relaxed groups/poor clusters, covering the temperature range 1-3 keV and selected to have the best available data, reveal a remarkable similarity in their temperature profile: cool cores outside of which the temperatures reach a peak for radii less than 0.1 of the virial radius and then decline. We fitted the derived mass profiles using an NFW model, which provides a good fit to the data when accounting for the central galaxy in the inner region. The concentration parameters and virial masses are in the range c = 5-22 and M = 2 x 10^13 - 4 x 10^14 solar masses, in general agreement with the concentrations found in numerical simulations. 
F. Gastaldello, D. Buote, P. Humphrey, L. Zappacosta, J. Bullock, F.   Brighenti, W. Mathews