Perseus cluster. However their study of the Coma, Virgo, and Ophiuchus clusters disfavour the DM nature of the line. @2015MNRAS.452.3905A excluded the existence of the DM decay line in the merged spectra of nearby galaxy halos, where the ratio of DM to baryonic, X-ray emitting matter, is expected to be higher [see also @2014PhRvD..90j3506M].

The Draco dwarf spheroidal galaxy was targeted by very deep observations with the *XMM-Newton* satellite. Depending on the modelling these observations are in tension with the dark matter interpretation of the line with $\rm{\sim 2\sigma}$ [see @2016MNRAS.458.3592J]. In the same dataset @2015arXiv151207217R found an upper limit on the sterile neutrino lifetime which is consistent (within $\rm{1-2~\sigma}$ uncertainties) with previous detections in the scenario that the sterile neutrinos with 7.1keV make up all DM in the halo. @2015MNRAS.450.2143J found evidence of a line around 3.5keV in *XMM-Newton* data of the Galactic centre. Other detections of the additional line include measurements of the Galactic center X-ray emission [@2015PhRvL.115p1301B]. The recent *XMM-Newton* flux measurements for an additional line in the 3.5keV regime in a sample of clusters of galaxies by @2015arXiv150805186I is in weak tension with our limits (e.g. $\sim2\sigma$ for Abell2199). @2015ApJ...810...48R used deep observations of the Bullet 