Generalized Lomb-Scargle periodograms of the HARPS SERVAL Doppler measurements and residuals. From top to bottom: RV data (upper panel); RV residuals following the subtraction of the Doppler signal of TOI-2427 b (second panel), TOI-2427 b plus the star rotation signal at 28 d (third panel), TOI-2427 b & c plus the star rotation signal at 28 d (fourth panel), TOI-2427 b & c plus the star rotation signals at 28 and 14 d (lower panel). The horizontal dotted lines mark the FAP at 0.1%, as derived using the bootstrap method. The vertical dashed blue and green lines mark the orbital frequencies of TOI-2427 b and c, respectively. The vertical dashed red lines mark the stellar rotation frequency at 1/28=0.036 d⁻¹ and its first two harmonics (1/14=0.071 d⁻¹. and.1/9.3=0.108 d⁻¹).