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

TL;DR

This paper reports the discovery of a sub-Uranus mass planet orbiting a host near the star-brown dwarf boundary, using dense microlensing data and detailed modeling to reveal its planetary nature and parameters.

Contribution

It presents the first detailed analysis of a microlensing planet around a host at the star-brown dwarf boundary, highlighting the technique's ability to detect such low-mass systems.

Findings

Planet has a mass lower than Uranus.

Host is near the star-brown dwarf boundary.

Two possible solutions due to degeneracy.

Abstract

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. 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: $(s, q)_{\rm inner} = [1.0883 \pm 0.0027, (3.125 \pm 0.248)\times 10^{-4}]$ for the inner solutions and $(s, q)_{\rm outer} = [1.0327 \pm 0.0054, (3.350 \pm 0.316)\times 10^{-4}]$ for the outer solutions. Using Bayesian analysis with constraints provided by the short event timescale ($t_{\rm E} \sim 9.1$~day) and the small angular Einstein radius ($\theta_{\rm E}\sim 0.16$~mas for the inner solution and $\sim 0.10$~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.