  We present results of a search for the 3.5 keV emission line in our recent
very long (~ 1.4 Ms) XMM-Newton observation of the Draco dwarf spheroidal
galaxy. The astrophysical X-ray emission from such dark matter-dominated
galaxies is faint, thus they provide a test for the dark matter origin of the
3.5 keV line previously detected in other massive, but X-ray bright objects,
such as galaxies and galaxy clusters. We do not detect a statistically
significant emission line from Draco; this constrains the lifetime of a
decaying dark matter particle to tau > (7-9) x 10^27 s at 95% CL (combining all
three XMM-Newton cameras; the interval corresponds to the uncertainty of the
dark matter column density in the direction of Draco). The PN camera, which has
the highest sensitivity of the three, does show a positive spectral residual
(above the carefully modeled continuum) at E = 3.54 +/- 0.06 keV with a 2.3
sigma significance. The two MOS cameras show less-significant or no positive
deviations, consistently within 1 sigma with PN. Our Draco limit on tau is
consistent with previous detections in the stacked galaxy clusters, M31 and the
Galactic Center within their 1-2 sigma uncertainties, but is inconsistent with
the high signal from the core of the Perseus cluster (which has itself been
inconsistent with the rest of the detections). We conclude that this Draco
observation does not exclude the dark matter interpretation of the 3.5 keV line
in those objects.
