denotes the properties of the ith cluster and $\rm{exp_i/exp_{tot}}$ is the fraction of the total exposure for the ith cluster. This is done for ACIS-I and ACIS-S separately (see weights in Tab. \[tab:clusterpars\]).

The most stringent limit on the mixing-angle from this analysis is $\rm{sin^2(2\Theta) \lesssim 10\times10^{-11}}$ (99.7 per cent confidence) for the merged ACIS-I spectra of the sample. All $\rm{3\sigma}$ (99.7 per cent) upper limits are compatible with the value of $\rm{sin^2(2\Theta) \sim 7\times10^{-11}}$ found for the full sample of @2014ApJ...789...13B. A simultaneous fit of the merged ACIS-I and ACIS-S spectrum did not improve the limits.

Discussion {#sec:discussion}
==========

[lrrrrrr]{} & & & & & &\
& & & & & &\

mergei & $\rm{-0.9^{+1.6}_{-1.6}}$ & $\rm{-12.7^{+22.8}_{-22.9}}$ & 0.06 & 0.11 & 2.08 & 0.197\
merges & $\rm{0.3^{+2.1}_{-2.2}}$ & $\rm{5.7^{+34.6}_{-37.0}}$ & 0.10 & 0.07 & 1.26 & 0.172\

\[tab:mix\]

We did not find evidence for an unidentified emission line at 3.55keV (see Fig. \[fig:lineall\]). The average value of the Gaussian flux measured in the cluster sample is consistent with zero with some scatter ($\rm{\chi^2_{red.}=1.6}$), suggesting mild additional systematic uncertainties ($\rm{\sim 25}$ per cent). This is a conservative estimate because the high $\rm{\chi^2_{red.}}$ value is mainly driven by outliers like 