Unabsorbed luminosity (in the 0.5–10 keV range) vs. the temperature (in keV) of the hot multicolour disk component for the XMM-Newton data (Table 2). The (red) solid curves correspond to internal temperature (T_in) of the accretion curtain versus total luminosity, as predicted by Mushtukov et al. (2017; see their Fig. 3). Different curves correspond to different magnetic field strength. From left to right it is 10¹², 2 × 10¹², 4 × 10¹², 8 × 10¹², 1.6 × 10¹³ and 3.2 × 10¹³ G.