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

TL;DR

The paper argues that the 3.5 keV X-ray line observed in galaxy clusters is due to atomic transitions in potassium, not sterile neutrino decay, based on spectral analysis and abundance considerations.

Contribution

It provides an alternative explanation for the 3.5 keV line, challenging the sterile neutrino dark matter hypothesis with spectral and abundance evidence.

Findings

K XVIII lines observed in solar flare spectra.

Potassium abundance in solar corona is higher than photospheric levels.

XMM-Newton spectra quality is too low to confirm sterile neutrino decay.

Abstract

Recent work by Bulbul et al. and Boyarsky et al. has suggested that a line feature at approx. 3.5 keV in the X-ray spectra of galaxy clusters and individual galaxies seen with XMM-Newton is due to the decay of sterile neutrinos, a dark matter candidate. This identification has been criticized by Jeltema and Profumo on the grounds that model spectra suggest that atomic transitions in helium-like potassium (K XVIII) and chlorine (Cl XVI) are more likely to be the emitters. Here it is pointed out that the K XVIII lines have been observed in numerous solar flare spectra at high spectral resolution with the RESIK crystal spectrometer and also appear in Chandra HETG spectra of the coronally active star sigma Gem. In addition, the solar flare spectra at least indicate a mean coronal potassium abundance which is a factor of between 9 and 11 higher than the solar photospheric abundance. This fact, together with the low statistical quality of the XMM-Newton spectra, completely accounts for the approx. 3.5 keV feature and there is therefore no need to invoke a sterile neutrino interpretation of the observed line feature at 3.5 keV.