Mrk 509 (left) and Mrk 841 (right) soft excess: data from 3 to 10 keV are fitted with a power law plus three Gaussian emission lines (see Table 2), and the model is then extrapolated to lower energies. Galactic absorption is taken into account. Only XIS1 data are shown, as they extend to 0.5 keV, but the analysis was performed using both FI and XIS1 data; the colour code for the different observations is as in Fig. 3. The energy on the abscissa is in the observer frame. The data were rebinned for clarity purposes.