for the fit with upper (blue) and lower (red) confidence limit of the Gaussian flux. For the effective-area curve see Fig. \[fig:fakelinemerge\].[]{data-label="fig:linemerge"}](merge_limit_s_unabs.pdf "fig:"){width="48.00000%"}

For every cluster we added the source and background spectra of every spatial bin from the maps (see Sect. \[sec:observations\], only inner regions with high surface brightness and homogeneous coverage for both ACIS-I/-S). The background was renormalised to match the count rate in the 10.0-12.5keV energy range. The response files were averaged and weighted by the number of counts in the spectrum (both auxiliary response files, ARF, and redistribution matrix files, RMF). For analysing the spectra we used `XSPEC` version 12.9.0 [@1996ASPC...99..409A] and ATOMDB version 2.0.2 [@2012ApJ...756..128F].

To estimate the upper limit of the flux allowed for an additional emission line, we searched for the best fitting `apec` model (with two temperature components) for collisionally-ionized plasma with absorption ($\rm{n_H}$) and an additional zero-width Gaussian line redshifted corresponding to the cluster distance (see Fig. \[fig:3.55all\] for spectra of individual clusters). The normalisation of the Gaussian was allowed to be negative to avoid bias. All spectra were grouped to contain a minimum of 22 raw counts in each bin (using `grppha`) and we used the range from 2-5keV for 