Probing the nature of dark matter with Cosmic X-rays: Constraints from   "Dark blobs" and grating spectra of galaxy clusters
  Gravitational lensing observations of galaxy clusters have identified dark matter ``blobs'' with remarkably low baryonic content. We use such a system to probe the particle nature of dark matter with X-ray observations. We also study high resolution X-ray grating spectra of a cluster of galaxies. From these grating spectra we improve the conservative constraints on a particular dark matter candidate, the sterile neutrino, by more than one order of magnitude. Based on these conservative constraints obtained from Cosmic X-ray observations alone, the low mass (m_s < 10keV) and low mixing angle (sin^2(2\theta) 10^{-6}) sterile neutrino is still a viable dark matter candidate. 
Signe Riemer-Sorensen, Kristian Pedersen, Steen H. Hansen, and Haakon   Dahle