Illustration of the pre-whitening process on the data in the pxx series. The top and bottom rows correspond to the data before and after pre-whitening, respectively. Left panels: Fourier transform of the full dataset, shown both with the inclusion and exclusion of the transit phases (brown and green colours, respectively). Note: the amplitude of the prewhitened spectrum (bottom left) is shown with a ten-fold increase. The frequencies detected by Period04 are shown by filled or empty circles, depending on whether the signal is present or not in the data. Right panels: corresponding folded synthetic dataset (light gray), as well as the data of the first orbital cycle (black).