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

¹ CERN, PH-TH, 1211 Geneve 23, Switzerland e-mail: alexey.boyarsky@epfl.ch
² École Polytechnique Fédérale de Lausanne, Institute of Theoretical Physics, FSB/ITP/LPPC, BSP 720, 1015 Lausanne, Switzerland
³ Bogolyubov Institute of Theoretical Physics, Kyiv, Ukraine
⁴ Helsinki University Observatory, Finland e-mail: jnevalai@astro.helsinki.fi
⁵ Institut des Hautes Études Scientifiques, 91440 Bures-sur-Yvette, France e-mail: ruchay@ihes.fr

Received: 20 November 2006
Accepted: 19 April 2007

Abstract

Aims.We improve the earlier restrictions on parameters of the warm dark matter (DM) in the form of a sterile neutrinos.

Methods.The results were obtained from not observing the DM decay line in the X-ray spectrum of the Milky Way (using the recent XMM-Newton PN blank sky data). We also present a similar constraint coming from the recent XMM-Newton observation of Ursa Minor – dark, X-ray quiet dwarf spheroidal galaxy.

Results.The new Milky way data improve on (by as much as the order of magnitude at masses ~3.5 keV) existing constraints. Although the observation of Ursa Minor has relatively poor statistics, the constraints are comparable to those recently obtained using observations of the Large Magellanic Cloud or M 31. This confirms a recent proposal that dwarf satellites of the MW are very interesting candidates for the DM search and dedicated studies should be made to this purpose.