Warm absorber transmission model (top) and lag-energy spectrum (bottom). The lag-energy spectrum from simulated data, at r = 10^15.75 cm (see Fig. 8) with an additive constant of 49.1 s, was fitted to the observed lag-energy spectrum, plotted in black, to obtain a χ² of 20.7 for 17 d.o.f. The simulated lag-energy spectrum with an offset, corresponding to the constant that resulted from the fit (~50 s), is overplotted in red. The reference band to compute the lag-energy spectrum is a broad EPIC-pn band (1.5−10 keV). We note that a negative lag indicates a soft lag, which means that the band of interest lags the broad reference band. This helps to easily match the lag-energy spectrum to the absorption features in the energy spectrum.