KMT-2024-BLG-1044L: A sub-Uranus microlensing planet around a host at the star–brown dwarf mass boundary

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
² Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
³ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁵ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁶ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁷ Center for Astrophysics | Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
⁸ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, China

^★ Corresponding author; cheongho@astroph.chungbuk.ac.kr

Received: 23 July 2024
Accepted: 2 November 2024

Abstract

Aims. We analysed microlensing data to uncover the nature of the anomaly that appeared near the peak of the short-timescale microlensing event KMT-2024-BLG-1044. Despite the anomaly’s brief duration of less than a day, it was densely observed through high-cadence monitoring conducted by the KMTNet survey.

Methods. Detailed modelling of the light curve confirmed the planetary origin of the anomaly and revealed two possible solutions, due to an inner–outer degeneracy. The two solutions provide different measured planet parameters: (s, q)_inner = [1.0883 ± 0.0027, (3.125 ± 0.248) × 10⁻⁴] for the inner solutions and (s, q)_outer = [1.0327 ± 0.0054, (3.350 ± 0.316) × 10⁻⁴] for the outer solutions.

Results. Using Bayesian analysis with constraints provided by the short event timescale (t_E ~ 9.1 day) and the small angular Einstein radius (θ_E ~ 0.16 mas for the inner solution and ~ 0.10 mas for the outer solutio), we determined that the lens is a planetary system consisting of a host near the boundary between a star and a brown dwarf and a planet with a mass lower than that of Uranus. The discovery of the planetary system highlights the crucial role of the microlensing technique in detecting planets that orbit substellar brown dwarfs or very low-mass stars.