Decaying dark matter in the Draco dwarf galaxy

Context. The sterile neutrino is an excellent dark matter candidate, which can be searched for in a wide range of astrophysical sites. It has previously been shown that the optimal search strategy is to consider dwarf galaxies belonging to the Milky Way. Aims. We search for line emission from decaying dark matter. Methods. We analyse publicly available Chandra X-ray observations of the dwarf galaxy Draco. Results. The Draco and blank sky (background) spectra are nearly identical in shape, which allows us to conclude: i) Dwarf spheroidals are ideal for studying dark matter X-ray emission since the baryonic noise is impressively low, ii) there is very little room for line emission, which leads to constraints in the mass-mixing angle parameter space of the sterile neutrino. We compare the standard flux derivation method to a very conservative rebinning approach. The resulting constraints are strongly dependent on the chosen method.