Suzaku search for evidence of sterile neutrinos in the Ursa Minor dwarf spheroidal galaxy

Abstract

We present results of our search for X‐ray line emission associated with the radiative decay of the sterile neutrino, a well‐motivated dark matter candidate, in Suzaku Observatory spectra of the Ursa Minor dwarf spheroidal galaxy. These data represent the first deep observation of one of these extreme mass‐to‐light systems and the first dedicated dark matter search using an X‐ray telescope. No such emission line is positively detected; and, we derive new upper limits that match or approach the best previous results over the entire 1–20 keV mass range from a single Suzaku observation. These are used to place constraints on the existence of sterile neutrinos with given combinations of mass and active‐sterile neutrino oscillation mixing angle in the general case, and in the case where they are assumed to constitute all of the dark matter. The allowed range implies that sterile neutrinos remain a viable candidate to make up some—or all—of the dark matter and also explain pulsar kicks and various other astrophysical phenomena.