Investigation of the 15.5 d signal Left: stacked BGLS periodogram of the residuals after fitting for the transiting planet. The colourbar on the right side indicates the instrument of the corresponding data point (orange: CARMENES, purple: IRD, green: HARPS). Right: TESS light curve phase-folded to the period and time of transit centre of GJ 3473 c as determined from the RVs. The saturated red shaded region indicates the expected transit, while the light red shaded region denotes the 68% credibility interval of the time of transit centre.