Width of FeKα (σ_line) versus the centroid energy (black squares). The black solid line traces a linear fit. We have marked in colour the expected width from the contribution of three different broadening phenomena: line blending, Compton broadening, and Doppler shifts, considering velocities of V(km s^-1) = 1000 (red) and V(km s^-1) = 2000 (green). Every single black square has an associated single red square and a single green square corresponding to the expected values of σ_line for that observation (see Sect. 4).