Coherence as a function of energy (U1-U3 left panel; O1-O2 right panel) over the frequency range 2.78 × 10⁻⁵ − 3.3 × 10⁻⁴ Hz, and with the 0.3 − 10 keV band as the reference band. Red shaded area in the right panel marks the 90% confidence level contours obtained from Cloudy simulations of an obscuring gas located at a distance of 10 light days, of electron density n_e = 2.6 × 10⁹ cm⁻³, and log N_H = 23.1, responding to the observed variations of the ionising continuum on timescales τ_rec <  1500 s. The ionisation parameter of the simulated obscuring gas varies within the range log ξ = 1.53 − 1.82 as a consequence of short timescale variations of the ionising continuum.