Periodogram of the SPIRou data. Top panel: generalised Lomb–Scargle (GLS) periodogram (Zechmeister & Kürster 2009) of the nightly averaged SPIRou velocities for TOI-4860 (red line). The horizontal lines represents 10, 1, and 0.1% false-alarm levels, from bottom to top. The vertical dotted green line marks the period of the transiting planet. Middle panel: idem after subtracting the Keplerian orbit of planet b. Given that the planet c candidate has a significant eccentricity, the power of the GLS periodogram is partially transferred to the harmonics of the orbital period, which leads to a reduced peak amplitude. Bottom panel: marginal posterior distribution of the period of a second planet search with SPIRou and ESPRESSO (Sect. 4.3).