Constraints on the parameters of radiatively decaying dark matter from the dark matter halo of the Milky Way and Ursa Minor

Using the recent XMM-Newton PN blank sky data, we improve the earlier restrictions on parameters of the warm dark matter (DM) in the form of sterile neutrino (by as much as the order of magnitude at masses ~ 3.5 kev). The results are obtained from non-observing DM decay line in the X-ray spectrum of the Milky Way. We also present similar constraint coming from the recent XMM-Newton observation of Ursa Minor -- dark, X-ray quiet dwarf spheroidal. Although this observation has relatively poor statistics, the constraints are comparable to those, recently obtained using observations of Large Magellanic Cloud or M31. This confirms recent proposal that dwarf satellites of the MW are very interesting candidates for the DM search and should be studied dedicatedly on this purpose.