Demonstration of the utility of spline detrending for periodicity searches. The top row includes I magnitude light curves for Source #2 (SXP 2.16), with the middle column using Savitzy-Golay detrending, and the right using spline detrending with wotan (Hippke et al. 2019). The corresponding periodograms and phase-folded data are shown below these light curves, with the established period from HS16 used in each. We show the Savitzky-Golay detrending using a window of 21 for the light curve and phase-folded data. As noted in Sect. 5.1, this value is also consistent with X-ray observations of the orbital period. The gray dotted line marks the false alarm level of 0.001.