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Recent work by Bulbul et al. and Boyarsky et al. has suggested that a linefeature at approx. 3.5 keV in the X-ray spectra of galaxy clusters andindividual galaxies seen with XMM-Newton is due to the decay of sterileneutrinos, a dark matter candidate. This identification has been criticized byJeltema and Profumo on the grounds that model spectra suggest that atomictransitions in helium-like potassium (K XVIII) and chlorine (Cl XVI) are morelikely to be the emitters. Here it is pointed out that the K XVIII lines havebeen observed in numerous solar flare spectra at high spectral resolution withthe RESIK crystal spectrometer and also appear in Chandra HETG spectra of thecoronally active star sigma Gem. In addition, the solar flare spectra at leastindicate a mean coronal potassium abundance which is a factor of between 9 and11 higher than the solar photospheric abundance. This fact, together with thelow statistical quality of the XMM-Newton spectra, completely accounts for theapprox. 3.5 keV feature and there is therefore no need to invoke a sterileneutrino interpretation of the observed line feature at 3.5 keV.

The X-Ray Line Feature At 3.5 Kev In Galaxy Cluster Spectra