The black hole mass in HLX-1. Left: the shaded areas indicate the 90% confidence interval for the mass estimation of the Chandra (grey), Swift (green), and XMM (blue) spectrum, respectively, given for the whole spin range. The three solid lines represent the black hole mass that corresponds to the spin a_∗ = 0.5 (where the error bars denote 90% confidence). The filled and open circles show previous mass measurements (see text for details). Right: the influence of spin on the mass estimation is shown for the Swift data. Error bars give the 90% confidence interval.