Relations between the parameters derived from our spectral fits, via the nthcomp (panels a)–c)) and compps models (panels d)–f)). Green, blue and red symbols are used to highlight the best-fitting model, according to our model selection criteria (Sect. 2.2). Blue: comptonization models with constrained T_e (Fig. 1a) further divided into hard (Γ ≤ 1.7; dark blue) and soft spectra (Γ > 1.7; light blue). Green: Comptonization models with unconstrained T_e (Fig. 1b). Red: p–value <0.05 fits. (Fig. 1c). Panel a) F_x−Γ diagram. We find a hard branch (dark blue points) where F_x and Γ are correlated, similar to the hard state in the BHB HID. At the highest fluxes in the outburst, we find the soft flaring branch (light blue points), similar to the BHB HID intermediate states. We also identify the softest spectra in our sample (Γ ≳ 2.4) with unconstrained T_e with a tentative ultra-luminous state (green points). The different branches also occupy characteristic regions in panel d) F_x−τ diagram, panels b, e), F_x–T_e diagrams, panel c) Γ −T_e diagram and panel f) τ −T_e diagram. The various parameter correlations are described in detail in Sect. 3.3.