Close view of the properties of the hard X-ray flare and subsequent X-ray plateau detected around MJD 55 199, derived fitting the source spectra with Comptonization models (nthcomp and compps). Panel a) time evolution of the source flux, F_x, in the 20–200 keV energy range (× 10^-8 erg cm^-2 s^-1) in comparison with the N_H evolution, where N_H is derived by leaving it as a free parameter in our fits, as described in Sect. 3.4. During the peak of the flare, when N_H displays lower values, it cannot be constrained by our fits. Panels b)–e) time evolution of the spectral parameters derived for this period. Panels f)–h) relations between the various nthcomp spectral parameters during this period. Panels i)–k) relations between the various compps spectral parameters during this period. For reference, we also show in panels f)–k) the complete dataset analysed in this work (grey points). In the diagrams in panels f)–k) we observe parameter correlations characteristic of the hard branch (see sect. 3.3). The dramatic changes in flux observed during this X-ray flare are accompanied by little variations in Γ and τ. Brief transitions to the soft flaring branch are observed during the peak of the flare. During the flare decay, the spectrum gradually softens, T_e decreases and τ displays high variability, while we observe a gradual increase in N_H, which reaches values close to 10²⁵ cm^-2 when the system reaches the bottom of the X-ray plateau. The spectral parameters derived during the X-ray plateau, occupy a separate region, as is evident in panels f)–h). Also, the parameter correlations reverse in the plateau branch with respect to the trends observed in the hard branch.