mass in the FOV of an observation by adding up the surface densities within the footprint of the extraction region for the spectra. The footprints of each observation and the maximum covered radius have been published by .

For we obtained an $\rm{M^{FOV}_{DM}}$ of $\rm{1.6\times10^{14}~M_{\odot}}$ [$\rm{2.75\times10^{14}~M_{\odot}}$ for $\rm{M_{2500}}$ given by @2006ApJ...640..691V]. We estimate the systematic uncertainties of $\rm{M^{FOV}_{DM}}$ to be 35 per cent on average due to scatter in the scaling relations for the total mass and scatter around the average concentration. The scatter will average out when adding together properties of the whole sample which means that we expect much smaller systematic uncertainties in the average $\rm{M^{FOV}_{DM}}$ used for limits on the merged cluster spectra (see Tab. \[tab:clusterpars\]).

Upper limits on 3.55keV line {#sec:lim}
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We investigated the possible existence of an unidentified X-ray emission line at $\rm{\sim3.55~keV}$ in the cluster spectra. We put limits on the existence of such a line in all the clusters individually and in a merged spectrum of the whole sample. A possible interpretation for this line has been the emission from decaying sterile neutrinos with a mass of $\rm{\sim7.1~keV}$ which could be a candidate for DM.

Limits in individual spectra {#sec:ind_lim}
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Fig. 