Distribution of X-ray luminosity produced from ADAFs around BHs without Keplerian accretion discs and the bolometric luminosity of the OB star companion, for two values of the viscous dissipation parameter δ = 0.001 (left panel) and 0.5 (right panel). The colour bar gives the predicted number of BH+OB star binaries in each pixel. The sum of the pixels in each panel is equal to unity. The solid black line shows the L_X, w = 10⁻⁷L_OB relation, with the dotted line and the dot-dashed line showing the ±1 dex range. The black and grey downward arrow denotes the upper limit to the X-ray luminosity from VFTS 827 and VFTS 243.