Deep XMM Observations of Draco rule out at the 99% Confidence Level a Dark Matter Decay Origin for the 3.5 keV Line

Abstract

We searched for an X-ray line at energies around 3.5 keV in deep, ~1.6 Msec XMM-Newton observations of the dwarf spheroidal galaxy Draco. No line was found in either the MOS or the PN detectors. The data in this energy range are completely consistent with a single, unfolded power law modeling the particle background, which dominates at these energies, plus instrumental lines; the addition of a ~3.5 keV line feature gives no improvement to the fit. The corresponding upper limit on the line flux rules out a dark matter decay origin for the 3.5 keV line found in observations of clusters of galaxies and in the Galactic Center at greater than 99% C.L..

5 pages, 3 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society; includes new discussion on Ruchayskiy et al (2015), arXiv:1512.07217