Relation between the photon index Γ and the normalisation of the power-law (pow) continuum as described in Sect. 3.1. The pow normalisation is shown in units of 10⁵² photons s^-1 keV^-1 at 1 keV. The data in green filled circles represent the Swift data from the obscured epoch (Feb. 2012 onwards), the blue open diamonds are the Swift data from the unobscured epoch of 2005 and 2007, the red open squares represent three XMM-Newton observations from unobscured epoch of 2000 and 2001, and the single filled magenta star corresponds to the stacked data from our summer 2013 campaign when the source was obscured. The data have been fitted with Eq. (3) shown in dashed black line.