Evolution of the photon index (Γ) of the intrinsic hot corona power law with respect to the Eddington ratio (λ_edd=L_bol/L_edd). The different colors represent different missions: green, Chandra; red, Chandra observation from 2010 evaluated from readout streak; blue, XMM-Newton; orange, Suzaku; brown solid line, linear regression best-fit in the softer-when-fainter state; brown dashed line, the uncertainty range of the linear fit. The soft-when-fainter trend is evident for log λ_Edd<−1.7.