We present TOI-1259Ab, a 1.0 Rjup gas giant planet transiting a 0.71 R⊙ K-dwarf on a 3.48 day orbit. The system also contains a bound white dwarf companion TOI-1259B with a projected distance of approximately 1600 AU from the planet host. Transits are observed in nine TESS sector and are 2.7 per cent deep - among the deepest known - making TOI-1259Ab a promising target for atmospheric characterization. Our follow-up radial velocity measurements indicate a variability of semiamplitude K = 71 ms-1, implying a planet mass of 0.44 Mjup. By fitting the spectral energy distribution of the white dwarf we derive a total age of 4.08+1.21-0.53 Gyr for the system. The K-dwarf's light curve reveals a rotational variability with a period of 28 days, which implies a gyrochronology age broadly consistent with the white dwarf's total age.
Final Version of Record not yet available as of 04/08/2021.
Accepted to MNRAS. Some structural changes from first arXiv version but no significant changes to results. One figure got a bit prettier