  Dark matter may be detected in X-ray decay, including from the decay of the
dark matter particles that make up the Milky Way (MW) halo. We use a range of
density profiles to compute X-ray line intensity profiles, with a focus on the
resonantly produced sterile neutrino dark matter candidate. Compared to the
Navarro--Frenk--White density profile, we show that using an adiabatically
contracted halo profile suppresses the line intensity in the halo outskirts and
enhances it in the Galactic Centre (GC), although this enhancement is
eliminated by the likely presence of a core within 3~kpc. Comparing our results
to MW halo observations, other X-ray observations, and structure formation
constraints implies a sterile neutrino mixing angle parameter
$s_{11}\equiv\sin^{2}(2\theta)\times10^{11}\sim[3,4]$ (particle lifetime
$\tau_{28}\equiv\tau/(10^{28}\mathrm{sec})\sim[1.0,1.3]$), which is
nevertheless is strong tension with some reported non-detections. We make
predictions for the likely decay flux that the XRISM satellite would measure in
the GC, plus the Virgo and Perseus clusters, and outline further steps to
determine whether the dark matter is indeed resonantly produced sterile
neutrinos as detected in X-ray decay.
