Top panel: Soft (0.3–0.7 keV) versus hard (0.9–10 keV) lags as a function of temporal frequency. By convention, negative lags correspond to the soft band lagging behind the hard band. Variability on timescales of 10⁴ s shows a soft lag of approximately 500 s. Bottom panel: Coherence as a function of frequency between the 0.3–0.7 and 0.9–10 keV bands. The blue-shaded region highlights the frequency range in which the soft band lags the hard band, during which the coherence remains close to 1. The blue-shaded frequency range was used to construct the energy–lag spectrum and the covariance spectrum. All statistical errors correspond to the 90% confidence level.