Top left: Fourier periodogram calculated from the Swift light curve, showing a clear peak at low frequencies. Significance levels of 0.1% and 0.01%, derived from tests (see text for details), are shown as dotted and dashed lines, respectively. Top right: comparison of period search results on the light curve composed of Swift data and scaled EPIC-pn data with different methods: the same peak (maxima for Fourier and AOV, minima for Renson, Lafler & Kinman, and conditional entropy) is detected in all cases and marked by a star. Bottom left: phase-folded X-ray light curve, using P = 107.99 d and T₀ = 2 458 288.654. Our 2018 Swift monitoring campaign of Schulte 12 is shown in green and other high-quality (error on count rate < 0.008 cts s⁻¹) Swift points in blue; EPIC-pn count rates divided by ten are shown as red stars; we note the good agreement between all data. Bottom right: same as previous, but with the lower-quality Swift data shown in dotted black.