Autocorrelation functions of the time series of the visible-light total brightness relating to each annulus at PA = 263°. The lag values refer to the time lag being considered. In each panel, the corresponding annulus identification number is reported in the top left. A light blue shaded area highlights the interval of 75–100 min where all the autocorrelation functions (except that obtained for annulus 1) exhibit a secondary maximum. In the bottom-right panel, referring to the annulus 10, a light green shaded area highlights the interval of 125–150 min where the autocorrelation function exhibits its third maximum.