Top: Evolution of the covering fraction from the time-resolved spectroscopic analysis using model 1 (Table A.1). The data points corresponding to the spectra shown in the lower panels are numbered and colour-coded. Middle and bottom: Selection of X-ray spectra from the time-resolved spectral analysis. Spectrum 4, corresponding to the C_f peak, is repeated in both panels. All X-ray spectra were re-binned for visual clarity.