Merged X-ray spectra (ACIS-I top and ACIS-S bottom) of the cluster sample with residuals of different fitted models. Fitted XSPEC models: apec+apec+zgauss with best fit (Bf), upper and lower confidence values (99.7 per cent) of the Gaussian flux in counts cm^-2 s^-1. The annotations show the best-fit value and the confidence interval obtained using MCMC. Residuals are shown for the fit with upper (blue) and lower (red) confidence limit of the Gaussian flux. For the effective-area curve see Fig. B.1.