Periodogram for normalised rates. Top: S-band dataset periodogram for the normalised rates model. The periodicity that this dataset yields is 163.1 ± 1.5 days. The purple arrows indicate some of the harmonics of the period. The dotted horizontal lines correspond to the 1σ and 2σ significance level determined by 10 000 bootstrap resamplings. The peak at 163.1 days is slightly above 2σ. Bottom: Folded normalised rates at the obtained frequency vs phase. Observations with detections are highlighted in magenta and the non-detections in grey. A little height was added to the non-detections for visualisation of phase domain coverage. No indication for a Gaussian-like activity window is present; however, the phase domain is not fully sampled.