KMT-2023-BLG-1431Lb: A New q<10^-4Microlensing Planet from a Subtle Signature

The current studies of microlensing planets are limited by small number statistics. Follow-up observations of highmagnification microlensing events can efficiently form a statistical planetary sample. Since 2020, the Korea Microlensing Telescope Network (KMTNet) and the Las Cumbres Observatory (LCO) global network have been conducting a follow-up program for high-magnification KMTNet events. Here, we report the detection and analysis of a microlensing planetary event, KMT-2023-BLG-1431, for which the subtle (0.05 mag) and short-lived (5 hr) planetary signature was characterized by the follow-up from KMTNet and LCO. A binary-lens single-source (2L1S) analysis reveals a planet/host mass ratio of q = (0.72 ± 0.07) × 10-4, and the single-lens binary-source (1L2S) model is excluded by ΔX2 = 80. A Bayesian analysis using a Galactic model yields estimates of the host star mass of Mhost = 0.57+0.33-0.29 M⊙, the planetary mass of Mplanet = 13.5+8.1-6.8 M⊙, and the lens distance of DL = 6.9+0.8-1.7 kpc. The projected planet-host separation of = a⊥ 2.3+0.5-0.5 au or = a⊥ 3.2+0.7-0.8, subject to the close/wide degeneracy. We also find that without the follow-up data, the survey-only data cannot break the degeneracy of central/resonant caustics and the degeneracy of 2L1S/1L2S models, showing the importance of follow-up observations for current microlensing surveys.