Vol. 592
In section 3. Cosmology

7.1 keV sterile neutrino constraints from X-ray observations of 33 clusters of galaxies with Chandra ACIS

by F. Hofmann, J.S. Sanders, K. Nandra, N. Clerc, and M. Gaspari A&A 592, A112

The recent indications for a weak unidentified emission line at 3.55 keV in X-ray spectra of clusters of galaxies have triggered a lot of interest in the community since the line could be explained by decay of dark matter in the form of sterile neutrinos with a mass of 7.1 keV. This article reports the analysis results of a large sample of 33 galaxy clusters observed with Chandra ACIS. The authors place an upper limit on the flux of the 3.55 keV line. Assuming all dark matter were made of 7.1 keV sterile neutrinos, the study finds no evidence for an unidentified emission line at 3.55 keV.