NGTS-39 b: A 58 d transiting warm Jupiter in an eccentric orbit

We report the discovery and characterisation of NGTS-39 b (TIC 453147896 b), a warm Jupiter transiting a Sun-like star on a 58.2 day, eccentric (e = 0.386 ± 0.019) orbit. NGTS-39 b was first identified from a TESS single transit event, and subsequently confirmed with NGTS photometry and radial velocity measurements from CORALIE and HARPS. The host star is a bright (Tmag = 11.02) F9 dwarf with effective temperature of Teff = $6053_{-30}^{+67}$ K. NGTS-39 b is a Jupiter-sized gas giant with a radius of 1.088 ± 0.012 RJ and a mass of 1.467 ± 0.081 MJ. Its equilibrium temperature is $519_{-5}^{+6}$ K, placing it between short-period hot Jupiters and cold, Jupiter-like giants. The high orbital eccentricity and intermediate equilibrium temperature of NGTS-39 b make it a valuable test case for formation and migration models, particularly in the poorly sampled regime of long-period gas giants. The RV data show a linear trend of $\dot{\gamma } = -17.75$ m s−1 yr−1, which indicates the presence of an outer companion. The discovery of NGTS-39 b contributes to the small but growing population of transiting warm Jupiters with P>50 days orbiting bright stars.