TVS and Fourier analysis of our time series of Hα line profiles. The top panel illustrates the mean profile on top of all the individual profiles (grey) as well as the TVS^1/2 (dashed line). The dotted line corresponds to the 1% significance level assessed from the S/N of the data in the continuum. A TVS^1/2 level above this threshold has a less than 1% probability of being due to a noise fluctuation. The dashed red line corresponds to the TVS^1/2 evaluated excluding the observations taken during the nights affected by the trough event (from HJD 2459422.6 to 2459425.9). The bottom left panel provides the Fourier periodogram as a function of wavelength divided by the 1% significance level. The colours indicate ratios of 0.5 (cyan), 1.0 (medium blue), 2.0 (dark blue), and 3.0 (violet). The periodogram divided by the 1% significance level averaged over the wavelength interval where significant variability occurs is shown by the rightmost panel. The dashed blue line corresponds to v₁.