Cross correlation of the Fe average charge with ionising luminosity for component 0 of NGC 3783. Top panel: Fe mean-subtracted average change (red curve) from the tpho calculation with a hydrogen number density of 10¹² m⁻³ and an ionising luminosity in black (t_bin = 10⁴ s). Bottom: correlativity from CCF versus lag. The blue vertical line marks the lag timescale of 5 × 10⁴ s corresponding to the largest correlativity.