KMT-2024-BLG-3237: Another Free-Floating Planet Candidate with Angular Einstein Radius Measurement

TL;DR

This paper reports the discovery of a free-floating planet candidate via gravitational microlensing, measuring its Einstein radius and estimating its mass, contributing to understanding isolated planetary objects.

Contribution

It presents a new free-floating planet candidate with angular Einstein radius measurement, enhancing the sample of such objects and providing insights into their properties.

Findings

Measured Einstein timescale of 0.54 days

Estimated lens mass around 67 Earth masses

Identified the lens as an isolated microlens

Abstract

Planet formation theories suggest the presence of free-floating planets (FFPs) that are ejected from their formation sites. While these planets emit very little light, they can be identified through gravitational microlensing. Here, we report the discovery of a FFP candidate in the microlensing event KMT-2024-BLG-3237. The observed light curve exhibits strong finite-source effects characterized by a small amplitude $(\lesssim 0.9\,{\rm mag})$ and a short timescale $(\lesssim 3\,{\rm days})$. The analysis yields an Einstein timescale of $t_{\rm E} = 0.54\pm0.02\,{\rm days}$ and an angular Einstein radius of $\theta_{\rm E} = 6.30\pm0.48\,\mu{\rm as}$. The measurements make it possible to estimate the lens mass as $M \simeq 102\,M_{\oplus}\,(\pi_{\rm rel}/16\,\mu{\rm as})^{-1}$, where $\pi_{\rm rel}$ is the relative lens-source parallax. Depending on the unknown $\pi_{\rm rel}$, the lens could be a Neptune-mass planet $(\pi_{\rm rel} \simeq 0.1\,{\rm mas})$ or a Saturn-mass planet $(\pi_{\rm rel} \simeq 16\,\mu{\rm as})$. A Bayesian analysis yields the lens mass $M = {67.3}_{-42.5}^{+103.2}\,M_{\oplus}$ and the lens distance $D_{\rm L} = {7.34}_{-2.11}^{+0.96}\,{\rm kpc}$. This lens is the eleventh isolated microlens with a measurement of $\theta_{\rm E} < 10\,\mu{\rm as}$. We find that additional searches for possible signatures of a lens host do not show significant evidence for the host.