Constraining Sterile Neutrino Dark Matter in the Milky Way Halo with Swift-XRT

Abstract

We present a search for sterile neutrino dark matter decay signals in the Milky Way’s dark matter halo by considering the entirety of the Swift X-ray Telescope (Swift-XRT) data archive. After filtering the raw archive, we analyze a ∼77 Ms data set containing the full field of view, as well as a ∼41 Ms data set with point sources excised using the Swift-XRT Point Source catalog. We report nondetections of emission lines across the 3–6 keV continuum in both data sets, including at and around 3.5 keV. The point-source-excised data set is found to have higher sensitivity to faint dark matter decay signals due to its freedom from point-source contamination and is thus used to set constraints. Nondetections across the total data set’s continuum are used to constrain the sterile neutrino dark matter parameter space, marginally strengthening existing X-ray constraints. Nondetections at ∼3.5 keV in data subsets grouped by angular distance from the galactic center are used to constrain the 3.5 keV line’s galactic intensity profile, providing the strongest constraints to date across ∼1/4 of the galaxy.