Illustration of spectral changes with the small dips. Top: comparison of spectra extracted during the bright intervals (black histogram) and during three smaller dips after the deep dip (light blue). The emission only deviates at intermediate wavelengths but is similar at long wavelengths (driven by N_H) and at short wavelengths (driven by T_eff and edge absorption). Bottom: Ad hoc model to attempt to reproduce this behaviour. The black curve represents a blackbody curve (in arbitrary flux units) with the best-fit parameters to the observed bright spectrum. The red curve represents the sum of the black curve, reduced by 10%, and a blackbody spectrum with a lower temperature but absorbed by the same N_H (see legend for values). The red model could be compared to the spectrum extracted during the smaller dips. See Sect. 6.1 for discussion.