Left panel: autocorrelation of the power spectrum as obtained by Fossat et al. (2017) as a function of frequency lag for three different time series of the average of photomultipliers PM1 and PM2 of GOLF sampled at 20 s (top), 60 s (middle) and 80 s (bottom); the bottom panel is comparable to Fig. 10 of Fossat et al. (2017). The green vertical lines correspond to frequencies of 210 nHz, 630 nHz and 1260 nHz. The black line indicates the mean value of the autocorrelation, while the orange line indicates the 10% probability level that there is at least one peak due to noise in the window; the level is 3.41σ. Right panel: sum of the correlation for l = 1, and l = 2 modes as obtained by Fossat et al. (2017) as a function of rotation frequency for three different time series sampled at 20 s (top), 60 s (middle) and 80 s (bottom); the bottom panel is comparable to Fig. 16 of Fossat et al. (2017). The black line indicates the mean value, while the orange line indicates the 10% probability level that there is at least one peak in the window due to noise; the level is 3.43σ.