Results of the time resolved spectral analysis carried out during the first part of the outburst decay. All spectra were fit with an absorbed blackbody model. We show in the three panels, from top to bottom, the blackbody temperature, radius, and the X-ray luminosity in units of 10³⁷ erg s^-1 for an assumed distance of 7.2 kpc (see Sect. 5.1). The luminosity has been computed from the source flux extrapolated in the 0.5−100 keV energy band (i.e., virtually bolometric for a blackbody spectral model with a temperature of ~3 keV) and corrected for absorption. The first point on the left is obtained from the fit to the BAT spectrum (in this case we also extrapolated the source flux in the 0.5−100 keV energy band; see Sect. 5.1).