Three Saturn-mass Microlensing Planets Identified through Signals from Peripheral-caustic Perturbations

TL;DR

This paper reports the discovery of three Saturn-mass planets around low-mass stars via microlensing, highlighting the method's effectiveness in detecting cold giants beyond the snowline at kiloparsec distances.

Contribution

It introduces a systematic approach to identify and confirm planetary signals from peripheral caustic perturbations in microlensing data, expanding the known population of cold giant planets.

Findings

Three Saturn-mass planets detected beyond the snowline.

Host stars are low-mass, 0.12-0.75 solar masses.

Planets have projected separations of 1.1-7.8 AU.

Abstract

We present the discovery and analysis of three microlensing planets identified through brief positive anomalies on the wings of their light curves. The events, KMT-2021-BLG-0852, KMT-2024-BLG-2005, and KMT-2025-BLG-0481, were detected in high-cadence survey data from the KMTNet, OGLE, MOA, and PRIME collaborations. The anomaly morphologies are consistent with major-image perturbations induced by planetary-mass companions located near the peripheral caustic. A systematic exploration of model degeneracies, including binary-source scenarios, higher mass-ratio binary lenses, and the inner--outer caustic degeneracy, firmly establishes the planetary origin of each signal. Measurements of the angular Einstein radius and event timescale, combined with Bayesian priors from a Galactic model, yield the physical parameters of each system. The hosts are low-mass stars (0.12--0.75~$M_\odot$), while the companions are Saturn-mass planets (0.16--0.59 $M_{\rm J}$) projected at separations of 1.1--7.8 au, placing them beyond the snowline of their hosts. These results demonstrate the capability of microlensing to detect and characterize cold giant planets around low-mass stars at kpc distances, populating the critical transition region between ice giants and gas giants.