Four Cold Super-Jupiters Revealed by Extended and Complex Microlensing Signals

TL;DR

This paper presents a systematic reanalysis of 2020–2025 KMTNet microlensing data to recover planets producing extended and complex anomalies, unveiling four cold, super-Jupiter-mass planets orbiting sub-solar hosts at several kiloparsecs. Each event is modeled with a 2L1S framework, yielding robust solutions with mass ratios in the range $q \sim (5$--$14)\times 10^{-3}$ and Einstein timescales $t_E \sim 20$–$45$ days, and subsequently constrained to physical parameters via Bayesian Galactic priors. The planets lie well beyond the snow line, highlighting microlensing as a powerful probe of cold giant planets at wide separations and illustrating the importance of thorough reanalysis to avoid biases in exoplanet demographics. Collectively, the work reinforces the role of extended anomalies in revealing planetary signals that automated searches may miss, informing future census efforts and planet formation theories for cold giants.

Abstract

We present the analysis of four microlensing events, KMT-2020-BLG-0202, KMT-2022-BLG-1551, KMT-2023-BLG-0466, and KMT-2025-BLG-0121, which exhibit extended and complex anomalies in their light curves. These events were identified through a systematic reanalysis of KMTNet data aimed at detecting planetary signals that deviate from the typical short-term anomaly morphology. Detailed modeling indicates that all four anomalies were produced by planetary companions to low-mass stellar hosts. The events have mass ratios of $q \sim (5$--$14)\times10^{-3}$ and Einstein timescales of $t_{\rm E} \sim 20$--$43$ days. Bayesian analyses based on Galactic models show that the companions are super-Jupiters with masses of a few to approximately 10 $M_{\rm J}$, orbiting sub-solar-mass hosts located at distances of $D_{\rm L} \sim 4$--$7$~kpc. All planets lie well beyond the snow line of their hosts, placing them in the regime of cold giant planets. These detections demonstrate that extended and complex microlensing anomalies, which are often challenging to recognize as planetary in origin, can nonetheless contain planetary signals. This work underscores the unique sensitivity of microlensing to cold, massive planets beyond the snow line and highlights the importance of systematic reanalyses of survey data for achieving a more complete and unbiased census of exoplanets in the Galaxy.

Figures (9)

• Figure 1: Light curve of the microlensing event KMT-2020-BLG-0202. The bottom panel presents the overall light curve, while the two upper panels show the zoomed-in view of the anomaly region and the residuals from the best-fit model (solid curve). The arrows labeled $t_1$, $t_2$, and $t_3$ in the top panel mark the times of the major anomalies. The left inset in the bottom panel illustrates the lens-system geometry, depicting the source trajectory (arrowed line) with respect to the caustic structure (red cuspy curve) generated by the binary lens. The source locations at the epochs of the major anomalies are indicated by labels matching those in the top panel. The right inset provides a magnified view of the configuration in the vicinity of $t_1$. The small green circles along the source trajectory mark the source positions at the epochs of data acquisition. Their sizes are scaled to the actual source size.
• Figure 2: $\Delta\chi^2$ maps in the $(s,q)$ grid-parameter space. The color scale indicates regions with $\Delta\chi^2 \leq n\times 1^2$ (red), $n\times 2^2$ (yellow), $n\times 3^2$ (green), and $n\times 4^2$ (cyan), where $n=10$ for KMT-2020-BLG-0202 and KMT-2022-BLG-1551, $n=4$ for KMT-2023-BLG-0466, and $n=15$ for KMT-2025-BLG-0121.
• Figure 3: Lensing light curve of KMT-2022-BLG-1551. Notations are consistent with those used in Fig. \ref{['fig:one']}. The two right insets in the bottom panel show zoomed-in views of the lens-system configurations around $t_1$ and $t_2$, respectively. The small circles along the source trajectory mark the source positions near the time of the anomaly, with their sizes scaled to the source radius and their colors matching those of the telescopes shown in the legend.
• Figure 4: Light curve of the lensing event KMT-2023-BLG-0466. The notation is the same as in Figure \ref{['fig:one']}.
• Figure 5: Distribution of the normalized source radius in the MCMC chain for KMT-2023-BLG-0466. The vertical solid line denotes the mean value, and the two dotted lines mark the 1$\sigma$ interval.