A Hot Neptune Candidate on a 3.15-Day Orbit Interior to the Giant-Planet Candidate TOI-7387.01

We report a second transiting-planet candidate in the TOI-7387 system (TIC 300381700), a T = 12.4, slightly evolved F9/G0 dwarf at about 600 pc that already hosts the 9.09-day giant-planet candidate TOI-7387.01. The new signal has a period of P = 3.1452736 ± 0.0000089 d and a depth of about 1000 ppm. It is detected in 69 transits in TESS 2-min photometry from Sectors 87–98 and is recovered independently in three full-frame-image pipelines (QLP, TGLC, TESS-SPOC) in every TESS observing year from 2018 to 2025. The SPOC pipeline flagged it as a threshold-crossing event in its Sector 1–96 multi-sector search, but it has not been released as a TOI. A joint transit model of both signals gives a radius of 4.62 ± 0.26 Earth radii, an orbital distance of 0.045 au and an equilibrium temperature of about 1610 K for the candidate. This places it inside the short-period Neptunian desert, on an orbit interior to a 14 ± 1 Earth-radius companion. The candidate passes odd/even, secondary-eclipse and period-alias tests. A point-spread-function fit to per-sector difference images excludes all 33 Gaia DR3 neighbours bright enough to produce the signal, and the depth does not change with aperture size. TRICERATOPS gives a false-positive probability of 0.013 ± 0.003, but the nearby false-positive probability (0.006 ± 0.001) is above the statistical-validation threshold because no high-resolution imaging of the star exists. We therefore present it as a planet candidate and describe the observations needed to validate it and measure its mass. The predicted radial-velocity semi-amplitude is about 8 m/s for a mass of about 19 Earth masses.