2010MNRAS.409L.128M

Some extensions of standard particle physics postulate that dark matter may be partially composed of weakly interacting sterile neutrino particles that have so far eluded detection. We use a short (∼5 ks) archival X-ray observation of Segue 1 obtained with the X-ray Telescope (XRT) onboard the Swift satellite to exclude the presence of sterile neutrinos in the 1.6-14 keV mass range down to a flux limit of 6x10^–12 erg/cm2/s within 67 pc of its centre. With an estimated mass-to-light ratio of ∼3400M_☉/L_☉, Segue 1 is the darkest ultrafaint dwarf galaxy currently measured. Spectral analysis of the Swift XRT data fails to find any non-instrumental spectral feature possibly connected with the radiative decay of a dark matter particle. Accordingly, we establish upper bounds on the sterile neutrino parameter space based on the non-detection of emission lines in the spectrum. The present work provides the most sensitive X-ray search for sterile neutrinos in a region with the highest dark matter density yet measured.