X-ray properties of the z ≃ 3 quasars. Left panel: continuum photon index against intrinsic flux density at rest-frame 2 keV, as measured in Paper I. The colour code is the same as that adopted in the previous figures. The dashed line represents the minimum photon index value (Γ_X = 1.7) adopted by RL19 to select the clean quasar sample for cosmology. Right panel: same for the intrinsic rest-frame flux integrated in the 2−10 keV band.