HydraA. The average of the calculated mixing-angle is much lower than the value of @2014ApJ...789...13B, but is consistent within the $\rm{3\sigma}$ upper limit (see Fig. \[fig:lineall\]).

The highest $\rm{3\sigma}$ upper limit and best fit is obtained for the spectrum of a $\rm{\sim 20~ks}$ ACIS-I observation of HydraA. The width of the fit line in this case is unusually broad (due to inaccuracies in the calibration files of the observation, ID 575 from 1999) and the line is not detected in a $\rm{\sim 200~ks}$ observation of the same cluster with ACIS-S (see Fig. \[fig:lineall\] for derived limits on mixing-angle).

A difference to the @2014ApJ...789...13B analysis is that we used only core regions of the clusters where the gas emission causes a higher background for detection of any DM line emission and we might thus be less sensitive. Using *Chandra* ACIS we could not extend the analysis to larger radii due to the limited FOV. Another difference in the analysis is that we did not use a separately weighted response for the Gaussian DM line for modelling the merged data.

@2015MNRAS.451.2447U used deep data taken with the *Suzaku* observatory and found some evidence for the predicted emission line in spectra of the 