stronger residuals in the real observations of ACIS-S could be that multi-temperature effects are stronger or that there are additional components not modelled by the current plasma emission model. As discussed in the paper there are two significant line-like residuals in ACIS-S at $\rm{\sim3.85~keV}$ and $\rm{\sim4.7~keV}$. The $\rm{\sim3.85~keV}$ residual could be explained by stronger than expected CaXIX emission lines (several lines known between $\rm{\sim3.86-3.90~keV}$). The $\rm{\sim4.7~keV}$ line could be due to TiXXI (see Sect. \[sec:discussion\]).

To test whether the two temperature fit is sufficient to obtain reliable 3.55keV line limits from the merged observations we modelled the two lines with additional Gaussian lines. The line-width was set to zero and the energy set to the two values estimated above. The goodness of fit improved from $\rm{\chi^2_{red.}=1.4}$ to 1.3 and the residual features seen in the original fit disappear (see Fig.\[fig:acissres\]). Both lines are detected at $\rm{>1\sigma}$.

The obtained limits on the 3.55keV flux however are very well consistent with the original fit showing that the additional residuals are negligible for our estimates.

![Merged X-ray spectrum (ACIS-S) of the cluster sample with residuals of different fitted models. Fitted `XSPEC` models: `apec+apec+zgauss(3.55keV) +zgauss(3.85keV) +zgauss(4.7keV)` with best-fit (Bf), upper and lower confidence values 