We initiate the systematic search for planets in the 2023 data of the Korea Microlensing Telescope Network (KMTNet), focusing on those planets found by the KMTNet AnomalyFinder with low preliminary estimates of the mass ratio, q < 2 & times; 10(-4). The 2023 season is the first for which the photometry of all events was re-reduced prior to the AnomalyFinder search, potentially increasing its sensitivity to planets. We find three strong low-q planet candidates, KMT-2023-BLG-0164 (q similar to 1.3 & times; 10(-4)), KMT-2023-BLG-1286 (q similar to 1.9 & times; 10(-4)), and KMT-2023-BLG-1746 (q similar to 8 & times; 10(-5)). KMT-2023-BLG-0164 is notable in that the source is projected on a very bright (I = 16.0) foreground star, which is either the planet's host or (more likely) a companion to the host. We obtain a spectrum, finding that its mass and distance are M similar to 1.0 M-circle dot and D similar to 1.5 kpc, respectively, the latter being the distance of the lens (D-L) regardless of whether the spectroscopic target is the host or its companion. We also analyze two other candidates, KMT-2023-BLG-0614 and KMT-2023-BLG-1593, which are unlikely to enter the statistical sample owing to their ambiguous interpretations as possible nonplanetary events.

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 similar to (5-14) x 10-3 and Einstein timescales of tE similar to 20-43 days. Bayesian analyses based on Galactic models show that the companions are super-Jupiters with masses of a few to approximately 10 MJ, orbiting sub-solar-mass hosts located at distances of DL similar to 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.

To complete the analysis of the 2023 KMTNet subprime-field microlensing planetary events identified by its AlertFinder system, we present the analysis of six events, KMT-2023-BLG-(1810, 0084, 1118, 0584, 1697, 2218). We find that the first three events are securely confirmed as planetary, with inferred mass ratios of log q ∼ -1.9, -2.0, and -2.6, respectively. The remaining three events exhibit the well-known degeneracy between binary-lens/single-source (2L1S) and single-lens/binary-source (1L2S) models, and two of these also admit viable stellar binary solutions. A Bayesian analysis indicates that the companions in the confirmed planetary events are likely either super-Jupiters orbiting beyond the snow line of M- or K-dwarf hosts or, for two degenerate solutions of KMT-2023-BLG-1118, Saturn-mass planets orbiting late-type M dwarfs. To date, the 2023 KMTNet sample contains 25 unambiguous planetary events, and its mass-ratio distribution is consistent with that of the KMTNet planetary sample from 2016–2019.

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 (less than or similar to 0.9 mag) and a short timescale (less than or similar to 3 days). The analysis yields an Einstein timescale of t(E) = 0.54 +/- 0.02 days and an angular Einstein radius of theta(E) = 6.30 +/- 0.48 mu as. The measurements make it possible to estimate the lens mass as M similar or equal to 102M(circle plus)(pi(rel)/16 mu as)(-1) , where pi(rel )is the relative lens-source parallax. Depending on the unknown pi(rel), the lens could be a Neptune-mass planet (pi(rel)similar or equal to 0.1 mas) or a Saturn-mass planet (pi(rel )similar or equal to 16 mu as). A Bayesian analysis yields the lens mass M=67.3(-42.5)(+103.2)M(circle plus) and the lens distance DL=7.34(-2.11)(+0.96)kpc . This lens is thirteenth isolated microlens with a measurement of theta(E) < 10 mu as. We find that additional searches for possible signatures of a lens host do not show significant evidence for the host.

To expand the homogeneous microlensing planetary sample of the Korea Microlensing Telescope Network (KMTNet), we investigate six planetary candidates identified by the AnomalyFinder search in the 2023 prime-field data, namely KMT-2023-BLG-1592, OGLE-2023-BLG-0766, KMT-2023-BLG-0332, KMT-2023-BLG-0486, KMT-2023-BLG-0792, and OGLE-2023-BLG-1043. Light-curve modeling indicates that the first two events have planetary mass ratios of logq similar to-3.0 and -2.6, while the third exhibits a brown dwarf mass ratio of logq similar to-1.4 . The remaining three events show the well-known degeneracy between the binary-lens single-source (2L1S) and single-lens binary-source (1L2S) interpretations. A Bayesian analysis yields companion masses of about 0.6 and 1.2 Jupiter masses for the two planetary systems, likely orbiting beyond the snow lines of M- or K-dwarf hosts. A review of the KMTNet planetary sample shows that candidates discovered by AnomalyFinder are significantly more likely to exhibit the 2L1S/1L2S degeneracy, consistent with the tendency of AnomalyFinder to detect subtler planetary signals.

We present observations and analysis of the bound planetary microlensing event KMT-2025-BLG-1616. The planetary signal was captured by the Korea Microlensing Telescope Network and the Dark Energy Camera Rogue Earths and Mars Survey (DREAMS). DREAMS’s minute-cadence observations break the central/resonant degeneracy in the binary-lens models. The color of the faint source star ( I = 22) is measured from the DREAMS’s r − z color. The planetary system has a planet-host mass ratio of q ∼ 5 × 10 ^−4 . A Bayesian analysis yields a host-star mass of ∼0.3 M _⊙ , a planetary mass of ∼40 M _⊕ , a projected planet-host separation of ∼1.6 au, and a lens distance of ∼7.5 kpc. Based on the photometric precision achieved by DREAMS for this event, we simulate free-floating planet (FFP) detections and find that DREAMS is sensitive to Mars-mass FFPs in the Galactic bulge and Moon-mass FFPs in the Galactic disk.

We report the discovery of four cold giant planets identified through the analysis of microlensing events detected by high-cadence surveys: OGLE-2016-BLG-0261, KMT-2025-BLG-0026, KMT-2025-BLG-0030, and KMT-2025-BLG-2272. The planetary signals appear as short-duration anomalies in the light curves and are well described by binary-lens single-source models with mass ratios between the lens components of order q ∼ 10^-3. Finite-source effects are securely measured in three out of four events, enabling determinations of the angular Einstein radius. A Bayesian analysis incorporating the measured event timescale and angular Einstein radius yields host masses of ∼ 0.07–0.6 M_⊙ and companion masses of ∼ 0.2–2.5 M_ J, confirming that all companions lie in the giant-planet regime. The projected separations are 0.7–6 au, placing all planets at or beyond the snow lines of their host stars. The inferred lens distances span ∼ 6.6–7.9 kpc, with all systems consistent with bulge lenses. These detections expand the sample of cold giant planets from homogeneous high-cadence surveys and highlight the sensitivity of microlensing to planetary systems beyond the snow line, providing further constraints on the occurrence and properties of giant planets around low-mass stars.

The Systematic KMTNet Planetary Anomaly Search series was conducted using the KMTNet data archived from 2016 to 2019. From this first phase of the series, we reported a total of 50 planetary systems hidden in the data archive, which represent about 35% of the total microlensing planets discovered from 2016 to 2019, demonstrating that this semi-machine-based search is a crucial channel for building a complete microlensing planet sample. We continue this series for 2021 and beyond to expand the microlensing planet sample. In this work for the 2021 KMTNet high-cadence fields (Prime fields), we find seven hidden planetary systems and three planet candidates. These new planets represent about 33% of the total microlensing planets discovered within the Prime fields observed during the 2021 bulge season. While the by-eye search is the primary channel for detecting microlensing planets (i.e., two-thirds of microlensing planet discoveries), this work clearly shows that a systematic search series is still necessary for constructing a complete microlensing planet sample. Such a sample is essential for conducting unbiased statistical studies of planet demographics in our Galaxy. Datasets for all the events used for analyses in this work are publicly available: doi:10.5281/zenodo.21472225.

We present observations and analysis of two low planet/host mass-ratio (q) microlensing planets discovered in high-magnification events. KMT-2025-BLG-0811Lb has q similar to 4.5 & times; 10(-5), and a Bayesian analysis favors a super-Earth/mini-Neptune orbiting an M- or K-dwarf host at a projected separation of similar to 3 au. KMT-2025-BLG-0912Lb has q = 2.6 & times; 10(-4) and likely hosts a super-Earth/mini-Neptune around either a low-mass M dwarf or a brown dwarf at similar to 1 au. Even with an observing cadence of Gamma > 30 hr(-1) during the planetary signal, KMT-2025-BLG-0811 still exhibits the "central-resonant" degeneracy. Reviewing nine such events, we find that the "central-resonant" degeneracy can be divided into two distinct types that occupy separate regions in the plane of q and normalized source radius (rho). Type I events have similar q but substantially different rho and are more difficult to resolve from the light curves. For Type II events, the "resonant" solutions have relatively lower q and larger rho. Our review provides guidance for searching for the alternative solution once one solution has been identified.

We present detailed light-curve analyses of 10 binary-lens microlensing events observed during the 2023-2025 seasons and selected as candidates for hosting brown dwarf companions. The sample includes OGLE-2023-BLG-0249, KMT-2023-BLG-1246, OGLE-2023-BLG-0079, KMT-2024-BLG-0072, KMT-2024-BLG-0897, KMT-2024-BLG-1876, KMT-2024-BLG-2379, KMT-2025-BLG-0922, KMT-2025-BLG-1056, and KMT-2025-BLG-2427. For each event, we carry out modeling of the light curve, explore relevant degeneracies, and, when finite-source effects are present, determine the angular Einstein radius. For OGLE-2023-BLG-0249, we additionally measure the microlens parallax, which allows a direct determination of the lens masses and distance. For the remaining events, we estimate the physical lens properties via Bayesian analyses incorporating Galactic priors. The resulting posteriors show that the lens companions in all systems have median masses in the brown dwarf regime, and the lenses of two events (KMT-2025-BLG-0922 and KMT-2025-BLG-1056) are consistent with binaries in which both lens components fall within the brown dwarf mass range. Spanning a wide range of projected separations and distances, these detections illustrate the power of high-cadence microlensing surveys to build a census of brown dwarf companions, including faint and distant systems beyond the reach of flux-limited methods.

In this work, we present analyses of four newly discovered planetary microlensing events from the 2024 KMTNet survey season: KMT-2024-BLG-0176, KMT-2024-BLG-0349, KMT-2024-BLG-1870, and KMT-2024-BLG-2087. In each case, the planetary nature was revealed through distinct types of anomalies in the lensing light curves: a positive bump near the peak for KMT-2024-BLG-0176, an asymmetric peak for KMT-2024-BLG-0349, a short-duration central dip for KMT-2024-BLG-1870, and a caustic-crossing feature for KMT-2024-BLG-2087. Detailed modeling of the light curves confirms that these anomalies are produced by planetary companions with planet-to-host mass ratios in the range of (1.5-17.9) x 10-3. Despite the diversity of signal morphologies, all planets detected in these events are giant planets with masses comparable to or exceeding that of Jupiter in the solar system. Each planet orbits a host star less massive than the Sun, emphasizing the strength of microlensing in uncovering planetary systems around low-mass stellar hosts.

We present observations and analyses of three high-magnification microlensing events: KMT-2022-BLG-0954, KMT-2024-BLG-0697, and MOA-2024-BLG-018. All three exhibit the 'Planet/Binary' degeneracy, with planetary solutions corresponding to mass ratios in the range-3.7 < log q < -2.2, while the binary solutions yield log q > -2.0. For KMT-2022-BLG-0954, we identify a previously unrecognized degeneracy among planetary solutions, involving different mass ratios and normalized source radii. In all three cases, single-lens binary-source models are excluded. Bayesian analyses suggest that the planetary solutions correspond to gas giants orbiting M/K dwarfs beyond the snow line, while KMT-2022-BLG-0954 also admits an alternative interpretation as a super-Earth orbiting a late-type M dwarf. The binary solutions imply a diverse set of systems, including M-dwarf pairs and M-dwarf-brown-dwarf binaries. A review of known events subject to the 'Planet/Binary' degeneracy shows that in most cases the degeneracy cannot be resolved through follow-up high-resolution imaging, particularly in the presence of the newly identified degeneracy.

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 circle dot), while the companions are Saturn-mass planets (0.16-0.59 MJ) 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.

We present the analysis of two planetary microlensing events, KMT-2025-BLG-0975 and KMT-2025-BLG-1160, discovered during the 2025 Galactic bulge microlensing season through high-cadence survey observations. In both events, short-duration anomalies near the peaks of the lensing light curves reveal the presence of planetary companions. Light-curve modeling yields planet-to-host mass ratios of q = 8.6 × 10^-4 for KMT-2025-BLG-0975 and 1.3 × 10^-4 for KMT-2025-BLG-1160. For KMT-2025-BLG-0975, finite-source effects are detected, enabling a measurement of the angular Einstein radius, whereas only a lower limit on this quantity is obtained for KMT-2025-BLG-1160. We estimate the physical parameters of the lens systems through Bayesian analyses constrained by the measured microlensing observables. The results indicate that the planetary companions have masses of M_ p=29.8^+50.5_-16.0 M_⊕ for KMT-2025-BLG-0975Lb and 25.4^+15.5_-14.1 M_⊕ for KMT-2025-BLG-1160Lb. Both planets have masses comparable to that of Uranus. The host stars are inferred to be a low-mass M dwarf with a mass of M_ h=0.10^+0.18_-0.06 M_⊙ for KMT-2025-BLG-0975L and a late K dwarf with a mass of M_ h=0.58^+0.35_-0.32 M_⊙ for KMT-2025-BLG-1160L. The projected planet–host separations are a_⊥=0.81^+0.10_-0.11 au for KMT-2025-BLG-0975Lb and a_⊥=2.56^+0.48_-0.71 au and 3.29^+0.61_-0.92 au for the inner and wide solutions, respectively, of KMT-2025-BLG-1160Lb. In both systems, the planets are located beyond the expected snow-line distances of their hosts, placing them in the cold ice-giant regime.

A population of free-floating planets is known from gravitational microlensing surveys. None have a directly measured mass, owing to a degeneracy with the distance, but the population statistics indicate that many are less massive than Jupiter. We report a microlensing event-KMT-2024-BLG-0792/OGLE-2024-BLG-0516, which was observed from both ground- and space-based telescopes-that breaks the mass-distance degeneracy. The event was caused by an object with 0.219-0.046+0.075 Jupiter masses that is either gravitationally unbound or on a very wide orbit. Through comparison with the statistical properties of other observed microlensing events and predictions from simulations, we infer that this object likely formed in a protoplanetary disk (like a planet), not in isolation (like a brown dwarf). Dynamical processes then ejected it from its birthplace, producing a free-floating object.

We present detailed analyses of three anomalous microlensing events—KMT-2021-BLG-0209, KMT-2021-BLG-0901, and OGLE-2025-BLG-0356—identified from a systematic reexamination of KMTNet light curves for which previous modeling attempts failed or left persistent residuals. Although all three events show caustic-related features consistent with binary-lens microlensing, we find that their full light-curve structures can be described by four-body configurations that required four-body configurations involving a binary lens and a binary source (2L2S). In KMT-2021-BLG-0209, weak caustic-exit residuals arise from a faint companion source undergoing an additional caustic interaction. In KMT-2021-BLG-0901, a late-time rebrightening is produced when the secondary source encounters the resonant caustic long after the primary. For OGLE-2025-BLG-0356, we test the degeneracy between system is described by a triple-lens single-source (3L1S) and 2L2S interpretations of a short isolated anomaly and find that the 2L2S model provides a significantly better fit. Source colors and magnitudes indicate binary sources composed of (G8V, M3V), (G8V, K2V), and (G6V, G8V) stars for the three events, respectively. Bayesian inference suggests that the lenses are predominantly low-mass binaries, including one system (KMT-2021-BLG-0901) with a companion consistent with a brown dwarf. These events add to the growing sample of well-characterized 2L2S systems and underscore the importance of systematically testing complex models, particularly in anticipation of the high-precision microlensing data expected from the Roman Space Telescope survey.

We analyze KMT-2025-BLG-2093, with angular Einstein radius θ_ E=13.1± 2.8 μ as, which makes it the second isolated microlens that lies in the “Einstein Desert” (9 μ as<θ_ E<25 μ as) between free-floating planets (FFPs) on one side and brown dwarfs and stars on the other. We discuss how its characteristics may give clues to future exploration of FFPs, especially in the era of satellite missions that have a major FFP focus, including Earth 2.0 and Roman.

The Earth's atmospheric turbulence degrades the precision of ground-based astrometry. Here, we discuss these limitations and propose that, with proper treatment of systematics and by leveraging the many epochs available from the Korean Microlensing Telescope Network (KMTNet), seeing-limited observations can reach sub-milliarcsecond precision. Such observations may be instrumental for the detection of Galactic black holes via microlensing. We present our methodology and pipeline for precise astrometric measurements using seeing-limited observations. The method is a variant of Gaia's Astrometric Global Iterative Solution that include several detrending steps. Tests on 6500 images of the same field, obtained by KMTNet with typical seeing condition of 1 arcsec and pixel scale of 0.4 arcsec, suggest that we can achieve, at the bright end (mag less than or similar to 17), per-epoch relative astrometric precision of similar to 5 mas and relative proper motion precision of 0.1-0.2 mas yr(-1) over a baseline of approximately five years, using data from the Cerro Tololo Inter-American Observatory (CTIO) site. Time binning on 5-20 d cadences improves the bright-source precision to similar to 2 mas per coordinate on astrometric microlensing-relevant time-scales. The precision is estimated using bootstrap simulations and further validated by comparing results from two independent KMTNet telescopes.

Analysis of binary-lens microlensing events typically requires intensive computation because of the multimodal and complex posterior distributions. With the recent development of the JAX-based differentiable binary-lensing modeling package microlux, we present an analysis of two microlensing events with planet/brown-dwarf candidates, KMT-2025-BLG-1314 and KMT-2025-BLG-1392. Both events exhibit the "Close/Wide" degeneracy, and KMT-2025-BLG-1314 suffers from the "Planet/Binary" degeneracy and a recently recognized "Point/Finite" degeneracy among the planetary solutions. For KMT-2025-BLG-1314, the binary mass ratio is log q similar to-3.5 for the planetary solutions and log q>-1.5 for the binary solutions, while for KMT-2025-BLG-1392 we find log q similar to-1.3 . We show that for the analysis of KMT-2025-BLG-1314, Hamiltonian Monte Carlo (HMC), enabled by microlux, provides robust parameter inference and outperforms traditional Markov chain Monte Carlo (MCMC) methods in the presence of bimodal posteriors.

We report the discovery and characterization of a planetary companion in the microlensing event KMT-2016-BLG-1337, which was produced by a binary system of low-mass stars. The light curve of the event exhibits a short-term anomaly superposed on the profile of a binary-lens single-source (2L1S) model. To investigate the nature of this anomaly, we performed detailed modeling under both the binary-lens binary-source (2L2S) and triple-lens single-source (3L1S) interpretations. The 3L1S model provides a substantially better fit to the data, strongly favoring the presence of a planetary companion in the lens system. Two viable 3L1S solutions describe the event nearly equally well. In one solution, the planet has a mass of M3 similar to 0.3 MJ and lies at a projected separation of a perpendicular to,3 similar to 4 au from the heavier member of the host binary. In the alternative solution, the planet has a mass of M3 similar to 7 MJ and a projected separation of a perpendicular to,3 similar to 1.5 au. The host binary consists of early M-type dwarfs with masses of M1 similar to 0.54 M circle dot and M2 similar to 0.40 M circle dot, separated in projection by a perpendicular to,2 similar to 3.5 au. The system is located at a distance of DL similar to 7 kpc toward the Galactic bulge. This event demonstrates the sensitivity of microlensing to planets in dynamically complex stellar environments, including systems beyond the reach of other detection techniques. It thereby contributes to a more comprehensive understanding of planet formation in multiple-star systems.