宮﨑 翔太

We introduce microJAX, the first fully differentiable implementation of the image-centered ray shooting algorithm for gravitational microlensing. Built on JAX and its XLA just-in-time compiler, microJAX exploits GPU parallelism while providing exact gradients through automatic differentiation. The current release supports binary- and triple-lens geometries, including limb-darkened extended-source effects, and delivers magnifications that remain differentiable for all model parameters. Benchmarks show that microJAX matches the accuracy of established packages and attains up to a factor of ∼5─6 speedup in the small-source, limb-darkened regime on an NVIDIA A100 GPU. Since the model is fully differentiable, it integrates seamlessly with probabilistic programming frameworks, enabling scalable Hamiltonian Monte Carlo and variational inference workflows. Although the present work focuses on standard microlensing magnification models, the modular architecture is designed to support upcoming implementations of microlensing higher-order effects, while remaining compatible with external likelihood frameworks that incorporate advanced noise models. microJAX thus provides a robust foundation for precise and large-scale surveys anticipated in the coming decade, including the Nancy Grace Roman Space Telescope, where scalable, physically self-consistent inference will be essential for maximizing scientific return....

We present the description of the instruments and the first results of the PRime-focus Infrared Microlensing Experiment (PRIME). PRIME is the first dedicated near-infrared (NIR) microlensing survey telescope located at the South African Astronomical Observatory (SAAO) in Sutherland, South Africa. Among its class, it offers one of the widest fields of view in the NIR regime. PRIME's main goals are (1) To study planetary formation by measuring the frequency and mass function of planets. In particular, we compare results from the central Galactic bulge (GB), accessible only in the NIR by PRIME, with those from the outer GB by optical surveys. (2) To conduct concurrent observations with NASA's Nancy Grace Roman Space telescope. Due to the different lines of sight between the ground and space, we detect slight variations in light curves, known as ``Space-based parallax." This effect allows us to measure the mass of lens systems and their distance from the Earth. It is the only method to measure the mass of the free-floating planets down to Earth-mass. We begin the GB survey in February 2024 and analyzed images through June 1, 2025, identifying 486 microlensing candidates and over a thousand variable stars, including Mira variables, which are useful to study the Galactic structure. We issue real-time alerts for follow-up observations, supporting exoplanet searches, and the chemical evolution studies in the GB. During the off-bulge season, we conduct an all-sky grid survey and Target of Opportunity (ToO) observations of transients, including gravitational wave events, gamma-ray bursts, and other science....

We introduce microJAX, the first fully differentiable implementation of the image-centered ray-shooting (ICRS) algorithm for gravitational microlensing. Built on JAX and its XLA just-in-time compiler, microJAX exploits GPU parallelism while providing exact gradients through automatic differentiation. The current release supports binary- and triple-lens geometries, including limb-darkened extended-source effects, and delivers magnifications that remain differentiable for all model parameters. Benchmarks show that microJAX matches the accuracy of established packages and attains up to a factor of $\sim$5-6 speed-up in the small-source, limb-darkened regime on an NVIDIA A100 GPU. Since the model is fully differentiable, it integrates seamlessly with probabilistic programming frameworks, enabling scalable Hamiltonian Monte Carlo and variational inference workflows. Although the present work focuses on standard microlensing magnification models, the modular architecture is designed to support upcoming implementations of microlensing higher-order effects, while remaining compatible with external likelihood frameworks that incorporate advanced noise models. microJAX thus provides a robust foundation for precise and large-scale surveys anticipated in the coming decade, including the Nancy Grace Roman Space Telescope, where scalable, physically self-consistent inference will be essential for maximizing scientific return....

Microlensing campaigns have a long history of observations covering the Galactic bulge, where thousands of detections have been obtained, including many exoplanetary systems. The Euclid Galactic Bulge Survey represents a unique opportunity to revisit a large number of past events and attempt the lens-source resolution of known events falling in the covered area. As the analysis of individual events requires non-negligible efforts, it is important to establish priorities among all possible targets, identifying those candidates with the higher chance for a successful resolution of the lens from the source and with the highest scientific interest. Drawing from the databases of the three main microlensing surveys (OGLE, MOA and KMTNet), we compile the complete catalog of past microlensing events in the Euclid survey footprint up to year 2023, containing 8081 entries. By re-modeling all events and cross-checking with Galactic models, we estimate the relative lens-source proper motions for all events. Taking into account all uncertainties, for each microlensing event we are able to estimate the probability that the lens is separated from the source by more than a given angular distance threshold. Hence, we rank all events by their resolution probability, providing additional useful information that will guide future analyses on the most promising candidates. A particular attention is dedicated to known planetary microlensing events....

Aims. We investigated binary-lens events from the 2022–2024 microlensing surveys, aiming to identify events suitable for lens mass measurements. We focused on two key light curve features: distinct caustic spikes with resolved crossings for measuring the angular Einstein radius (θ_E), and long durations enabling microlens-parallax (π_E) measurements. Four events met these criteria: KMT-2022-BLG-1479, KMT-2023-BLG-0932, OGLE-2024-BLG-0142, and KMT-2024-BLG-1309. Methods. We estimated the angular Einstein radius by combining the normalized source radius measured by modeling the resolved caustic spikes with the angular source radius derived from the source color and magnitude. Additionally, we determined the microlens parallax through light curve modeling, taking higher-order effects caused by the orbital motions of Earth and the binary lens into consideration. Results. With measurements of the event timescale, angular Einstein radius, and microlens parallax, we uniquely determined the mass and distance of the lens. For the events KMT-2022-BLG-1479, KMT-2023-BLG-0932, and KMT-2024-BLG-1309, both components of the binary lens have masses lower than that of the Sun, consistent with M-type dwarfs, which are the most common type of lenses in Galactic microlensing events. These lenses are relatively nearby, with distances of ≲2.5 kpc, indicating their location within the Galactic disk. In contrast, for OGLE-2024-BLG-0142, the primary lens component has a mass similar to that of the Sun, while the companion lens component has about half the mass of the primary. This lens system is situated at a greater distance, roughly 4.5 kpc....

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....

As part of the Galactic Bulge Time Domain Survey (GBTDS), the Nancy Grace Roman Galactic Exoplanet Survey (RGES) will use microlensing to discover cold outer planets and free-floating planets unbound to stars. NASA has established several science requirements for the GBTDS to ensure RGES success. A key advantage of RGES is Roman's high angular resolution, which will allow detection of flux from many host stars. One requirement specifies that Roman must measure the masses and distances of 40% of detected planet hosts with 20% precision or better. To test this, we simulated microlensing events toward the GBTDS fields and used Fisher matrix analysis to estimate light curve parameter uncertainties. Combining these with Roman imaging observables (lens flux, relative lens-source proper motion), we estimated the achievable precision of lens mass and distance measurements. Using pyLIMASS, a publicly available code for estimating lens properties, we applied this analysis to 3,000 simulated events. Assuming the Cassan et al. (2012) exoplanet mass function, we find that >40% of host stars meet the required 20% precision threshold, confirming that the GBTDS can satisfy the mission requirement. We validated our approach by comparing our inferred lens masses and distances to empirical measurements from detailed image-constrained light curve modeling of historical microlensing events with Hubble and Keck follow-up imaging. Our results agree within roughly 1 sigma, demonstrating that both approaches yield consistent and reliable mass and distance estimates, and confirming the robustness of our simulations for Roman-era microlensing science....

In this study, we analyze microlensing events from the 2023 and 2024 observing seasons to identify cases likely caused by binary systems composed of BDs. By applying criteria that the binary-lens events exhibit well-resolved caustics, short time scales ($t_{\rm E} \lesssim 9$ days), and have small angular Einstein radii ($θ_{\rm E} \lesssim 0.17$~mas), we identify six candidate binary BD events: MOA-2023-BLG-331, KMT-2023-BLG-2019, KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486. Analysis of these events leads to models that provide precise estimates for both lensing observables, $t_{\rm E}$ and $θ_{\rm E}$. We estimate the masses of the binary components through Bayesian analysis, utilizing the constraints from $t_{\rm E}$ and $θ_{\rm E}$. The results show that for the events KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486, the probability that both binary components lie within the BD mass range exceeds 50\%, indicating a high likelihood that the lenses of these events are binary BDs. In contrast, for MOA-2023-BLG-331L and KMT-2023-BLG-2019L, the probabilities that the lower-mass components of the binary lenses lie within the BD mass range exceed 50\%, while the probabilities for the heavier components are below 50\%, suggesting that these systems are more likely to consist of a low-mass M dwarf and a BD. The brown-dwarf nature of the binary candidates can ultimately be confirmed by combining the measured lens-source relative proper motions with high-resolution imaging taken at a later time....

Aims. We present analyses of six microlensing events: KMT-2023-BLG-0548, KMT-2023-BLG-0830, KMT-2023-BLG-0949, KMT-2024-BLG-1281, KMT-2024-BLG-2059, and KMT-2024-BLG-2242. These were identified in KMTNet data from the 2023–2024 seasons, selected for exhibiting anomalies shorter than one day – potential signatures of low-mass planetary companions. Motivated by this, we conducted detailed investigations to characterize the nature of the observed perturbations. Methods. Detailed modeling of the light curves reveals that the anomalies in all six events are caused by planetary companions to the lenses. The brief durations of the anomalies are attributed to various factors: a low planet-to-host mass ratio (KMT-2024-BLG-2059, KMT-2024-BLG-2242), a wide planet-host separation (KMT-2023-BLG-0548), small and elongated caustics restricting the source's interaction region (KMT-2023-BLG-0830, KMT-2024-BLG-1281), and a partial caustic crossing (KMT-2023-BLG-0949). Results. We estimated the physical parameters of the lens systems using Bayesian analysis. For KMT-2023-BLG-0548, the posterior distribution of the lens mass shows two distinct peaks: a low-mass solution indicating a sub-Jovian planet orbiting an M dwarf in the Galactic disk, and a high-mass solution suggesting a super-Jovian planet around a K-type dwarf in the bulge. KMT-2023-BLG-0830 hosts a Neptune-mass planet orbiting an M dwarf in the Galactic bulge. KMT-2023-BLG-0949 involves a super-Jovian planet orbiting a ~0.5 M_⊙ host located at ~6 kpc. KMT-2024-BLG-2059Lb is a super-Earth with a mass about seven times that of Earth, orbiting an early M dwarf of ~0.5 M_⊙. KMT-2024-BLG-1281L hosts a planet slightly more massive than Neptune, orbiting an M dwarf of ~0.3 M_⊙. The short timescale and small angular Einstein radius of KMT-2024-BLG-2242 suggest a ~0.07 M_⊙ primary, likely a brown dwarf, with a planet of Uranus- or Neptune-like mass....

We present the analysis of a microlensing event KMT-2022-BLG-0086 of which the overall light curve is not described by a binary-lens single-source (2L1S) model, which suggests the existence of an extra lens or an extra source. We found that the event is best explained by the binary-lens binary-source (2L2S) model, but the 2L2S model is only favored over the triple-lens single-source (3L1S) model by Δχ² ≃ 9. Although the event has noticeable anomalies around the peak of the light curve, they are not enough covered to constrain the angular Einstein radius θ_E, thus we only measure the minimum angular Einstein radius <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>θ</mml:mi></mml:mrow><mml:mrow><mml:mi>E</mml:mi><mml:mo>,</mml:mo><mml:mi>min</mml:mi></mml:mrow></mml:msub></mml:math> </inline-formula>. From the Bayesian analysis, it is found that that the binary lens system is a binary star with masses of <inline-formula> <mml:math><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo><mml:mo>=</mml:mo><mml:mo>(</mml:mo><mml:mn>0.4</mml:mn><mml:msubsup><mml:mrow><mml:mn>6</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.25</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.35</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mn>0.7</mml:mn><mml:msubsup><mml:mrow><mml:mn>5</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.55</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.67</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:math> </inline-formula> at a distance of <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mi>L</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>5.8</mml:mn><mml:msubsup><mml:mrow><mml:mn>7</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1.79</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>1.21</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula> kpc, while the triple lens system is a brown dwarf or a massive giant planet in a low-mass binary-star system with masses of <inline-formula> <mml:math><mml:mo>(</mml:mo><mml:msub><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mrow><mml:mi>m</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub><mml:mo>)</mml:mo><mml:mo>=</mml:mo><mml:mo>(</mml:mo><mml:mn>0.4</mml:mn><mml:msubsup><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.35</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.41</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub><mml:mo>,</mml:mo><mml:mn>0.05</mml:mn><mml:msubsup><mml:mrow><mml:mn>6</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.047</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.055</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula>, <inline-formula> <mml:math><mml:mn>20.8</mml:mn><mml:msubsup><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>17.04</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>20.20</mml:mn></mml:mrow></mml:msubsup><mml:mspace></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mi>J</mml:mi></mml:mrow></mml:msub><mml:mo>)</mml:mo></mml:math> </inline-formula> at a distance of <inline-formula> <mml:math><mml:msub><mml:mrow><mml:mi>D</mml:mi></mml:mrow><mml:mrow><mml:mi>L</mml:mi></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>4.0</mml:mn><mml:msubsup><mml:mrow><mml:mn>6</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>3.28</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>1.39</mml:mn></mml:mrow></mml:msubsup></mml:math> </inline-formula> kpc, indicating a disk lens system. The 2L2S model yields the relative lens-source proper motion of μ_rel ≥ 4.6 mas yr^‑1 that is consistent with the Bayesian result, whereas the 3L1S model yields μ_rel ≥ 18.9 mas yr^‑1, which is more than three times larger than that of a typical disk object of ∼6 mas yr^‑1 and thus is not consistent with the Bayesian result. This suggests that the event is likely caused by the binary-lens binary-source model....

Aims. The light curves of the microlensing events MOA-2022-BLG-091 and KMT-2024-BLG-1209 exhibit anomalies with very similar features. These anomalies appear near the peaks of the light curves, where the magnifications are moderately high, and are distinguished by weak caustic-crossing features with minimal distortion while the source remains inside the caustic. To achieve a deeper understanding of these anomalies, we conducted a comprehensive analysis of the lensing events. Methods. We carried out binary-lens modeling with a thorough exploration of the parameter space. This analysis revealed that the anomalies in both events are of planetary origin, although their exact interpretation is complicated by different types of degeneracy. In the case of MOA-2022-BLG-091, the main difficulty in the interpretation of the anomaly arises from a newly identified degeneracy related to the uncertain angle at which the source trajectory intersects the planet–host axis. For KMT-2024-BLG-1209, the interpretation is affected by the previously known inner-outer degeneracy, which leads to ambiguity between solutions in which the source passes through either the inner or outer caustic region relative to the planet host. Results. Bayesian analysis indicates that the planets in both lens systems are giant planets with masses about two to four times that of Jupiter, orbiting early K-type main-sequence stars. Both systems are likely located in the Galactic disk at a distance of around 4 kiloparsecs. The degeneracy in KMT-2024-BLG-1209 is challenging to resolve because it stems from intrinsic similarities in the caustic structures of the degenerate solutions. In contrast, the degeneracy in MOA-2022-BLG-091, which occurs by chance rather than from inherent characteristics, is expected to be resolved by the future space based Roman RGES microlensing survey....

We present a comprehensive analysis of the planetary microlensing event OGLE-2015-BLG-1609. The planetary anomaly was detected by two survey telescopes, OGLE and MOA. Both surveys collected enough data over the planetary anomaly to enable an unambiguous planet detection. Such survey detections of planetary anomalies are needed to build a robust sample of planets, which could improve studies on the microlensing planetary occurrence rate by reducing biases and statistical uncertainties. In this work we examined different methods for modeling microlensing events using individual datasets. In particular, we incorporated a Galactic model prior to better constrain the poorly defined microlensing parallax. Ultimately, we fitted a comprehensive model to all available data, identifying three potential topologies, with two showing comparably high Bayesian evidence. Our analysis indicates that the host of the planet is either a brown dwarf, with a probability of 34%, or a low-mass stellar object (M dwarf), with a probability of 66%. The topology that provides the best fit to the data results in an extraordinary low host mass, M_h = 0.025^+0.050_-0.012M_⊙, &lt;!--inline-formula id="FI1"&gt;&lt;alternatives&gt;<tex-math id="tex_eq1">&lt;![CDATA[$\[0.025_{-0.012}^{+0.050}\]$]]&gt;</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="mml_eq1"><mml:msubsup><mml:mn>0.025</mml:mn><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>‑</mml:mo><mml:mn>0.012</mml:mn></mml:mrow><mml:mrow class="MJX-TeXAtom-ORD"><mml:mo>+</mml:mo><mml:mn>0.050</mml:mn></mml:mrow></mml:msubsup></mml:math>&lt;inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" id="img_eq1" mime-subtype="png" mimetype="image" xlink:href="aa53454-24-eq1.png"/&gt;&lt;/alternatives&gt;</inline-formula--> accompanied by an Earth-mass planet with M_c = 1.9^+3.9_-1.0M_⊕....

In this work, we continue to apply the updated KMTNet tender-love care photometric pipeline to historical microlensing events. We apply the pipeline to a subsample of events from the KMTNet database, which we refer to as the giant source sample. Leveraging the improved photometric data, we conduct a systematic search for anomalies within this sample. The search successfully uncovers four new planet-like anomalies and recovers two previously known planetary signals. After detailed analysis, two of the newly discovered anomalies are confirmed as clear planets: KMT-2019-BLG-0578 and KMT-2021-BLG-0736. Their planet-to-host mass ratios are q ∼ 4 × 10^‑3 and q ∼ 1 × 10^‑4, respectively. Another event, OGLE-2018-BLG-0421 (KMT-2018-BLG-0831), remains ambiguous. Both a stellar companion and a giant planet in the lens system could potentially explain the observed anomaly. The anomaly signal of the last event, MOA-2022-BLG-038 (KMT-2022-BLG-2342), is attributed to an extra source star. Within this sample, our procedure doubles the number of confirmed planets, demonstrating a significant enhancement in the survey sensitivity....

We present the discovery and analysis of the sixth microlensing two-planet system, KMT-2022-BLG-1818Lb,c, detected by a follow-up program targeting high-magnification events. Both planets are subject to the well-known ''Close/Wide'' degeneracy, although for the first planet, which has a super-Jovian mass ratio of $q_2 \simeq 5\times 10^{-3}$ in both solutions, the Close topology, with a normalized separation of $s\simeq 0.70$, is clearly preferred by $Δχ^2=26$. However, contrary to all previous two-planet microlensing systems, the mass ratio for the second planet, $q_3$, is substantially (factor of $\sim 10$) different for the Close and Wide topologies of the first planet. While this degeneracy is resolved in the present case due to high-cadence follow-up observations, the appearance of this new degeneracy indicates the need for caution in the analysis of future two-planet systems. A Bayesian analysis suggests that the host is likely a K-dwarf star in the Galactic disk. The first planet is probably a super-Jupiter on a Jupiter-like orbit, while the second planet is a Saturn-class planet on either a Mercury-like or Saturn-like orbit....

Aims. The United Kingdom Infrared Telescope (UKIRT) microlensing survey was conducted over four years, from 2016 to 2019, with the goal of serving as a precursor to future near-infrared microlensing surveys. Focusing on stars in the Galactic center and utilizing near-infrared passbands, the survey identified approximately one thousand microlensing events, 27 of which displayed anomalies in their light curves. This paper presents an analysis of these anomalous events, aiming to uncover the underlying causes of the observed anomalies. Methods. The events were analyzed under various configurations, considering the potential binarity of both the lens and the source. For 11 events that were additionally observed by other optical microlensing surveys, including those conducted by the OGLE, KMTNet, and MOA collaborations, we incorporated their data into our analysis. Results. Among the reported anomalous events, we revealed the nature of 24 events except for three events, in which one was likely to be a transient variable, and two were difficult to accurately characterize their nature due to the limitations of the available data. We confirmed the binary lens nature of the anomalies in 22 events. Among these, we verified the earlier discovery that the companion in the binary lens system UKIRT11L is a planetary object. Accurately describing the anomaly in UKIRT21 required a model that accounted for the binarity of both the lens and the source. For two events UKIRT01 and UKIRT17, the anomalies could be interpreted using either a binary-source or a binary-lens model. For the UKIRT05, it was found that accounting for higher-order effects induced by the orbit al motions of both Earth and the binary lens was crucial. With the measured microlensing parallax togeter with the angular Einstein radius, the component masses of the UKIRT05 binary lens were determined to be M₁ = (1.05 ± 0.20) M_⊙, M₂ = (0.36 ± 0.07) M_⊙, and the distance to the lens was found to be D_L = (3.11 ± 0.40) kpc....

Exoplanets classified as super-Earths are commonly observed on short-period orbits, close to their host stars, but their abundance on wider orbits is poorly constrained. Gravitational microlensing is sensitive to exoplanets on wide orbits. We observed the microlensing event OGLE-2016-BLG-0007, which indicates an exoplanet with a planet-to-star mass ratio roughly double the Earth-Sun mass ratio, on an orbit longer than Saturn's. We combined this event with a larger sample from a microlensing survey to determine the distribution of mass ratios for planets on wide orbits. We infer that there are ~0.35 super-Earth planets per star on Jupiter-like orbits. The observations are most consistent with a bimodal distribution, with separate peaks for super-Earths and gas giants. We suggest that this reflects differences in their formation processes....

Aims. We examined the anomalies in the light curves of the lensing events MOA-2022-BLG-033, KMT-2023-BLG-0119, and KMT- 2023-BLG-1896. These anomalies share similar traits: they occur near the peak of moderately to highly magnified events and display a distinct short-term dip feature. Methods. We conducted detailed modeling of the light curves to uncover the nature of the anomalies. This modeling revealed that all signals originated from planetary companions to the primary lens. The planet-to-host mass ratios are very low: q ~ 7.5 × 10^‑5 for MOA-2022-BLG-033, q ~ 3.6 × 10^‑4 for KMT-2023-BLG-0119, and q ~ 6.9 × 10^‑5 for KMT-2023-BLG-1896. The anomalies occurred as the source passed through the negative deviation region behind the central caustic along the planet-host axis. The solutions are subject to a common inner-outer degeneracy, which results in varying estimations of the projected planet-host separation. For KMT-2023-BLG-1896, although the planetary scenario provides the best explanation for the anomaly, the binary companion scenario is possible. Results. We estimated the physical parameters of the planetary systems through Bayesian analyses based on the lensing observables. While the event timescale was measured for all events, the angular Einstein radius was not measured for any. Additionally, the microlens parallax was measured for MOA-2022-BLG-033. The analysis identifies MOA-2022-BLG-033L as a planetary system with an ice giant with a mass of approximately 12 times that of Earth orbiting an early M dwarf star. The companion of KMT-2023-BLG-1896L is also an ice giant, with a mass of around 16 Earth masses, orbiting a mid-K-type main-sequence star. The companion of KMT-2023-BLG- 0119L, which has a mass around that of Saturn, orbits a mid-K-type dwarf star. The lens for MOA-2022-BLG-033 is highly likely to be located in the disk, whereas for the other events the probabilities of the lens being in the disk or the bulge are roughly equal....

We present measurements of the microlensing optical depth and event rate toward the Galactic bulge using the data set from the 2006 to 2014 MOA-II survey, which covers 22 bulge fields spanning ∼42 deg² between ‑5° &lt; l &lt; 10° and ‑7° &lt; b &lt; ‑1°. In the central region with ∣l∣ &lt; 5°, we estimate an optical depth of <inline-formula> </inline-formula> and an event rate of Γ = [16.08 ± 0.28] × 10^‑6<inline-formula> </inline-formula> using a sample consisting of 3525 microlensing events, with Einstein radius crossing times of t_E &lt; 760 days and a source star magnitude of I_s &lt; 21.4 mag. We confirm our results are consistent with the latest measurements from the OGLE-IV 8 yr data set. We find our result is inconsistent with a prediction based on Galactic models, especially in the central region with ∣b∣ &lt; 3°. These results can be used to improve the Galactic bulge model, and more central regions can be further elucidated by upcoming microlensing experiments, such as the PRime-focus Infrared Microlensing Experiment and Nancy Grace Roman Space Telescope....

Gravitational microlensing is a phenomenon that allows us to observe the dark remnants of stellar evolution, even if these bodies are no longer emitting electromagnetic radiation. In particular, it can be useful to observe solitary neutron stars or stellar-mass black holes, providing a unique window through which to understand stellar evolution. Obtaining direct mass measurements with this technique requires precise observations of both the change in brightness and the position of the microlensed star. The European Space Agency's Gaia satellite can provide both. Using publicly available data from different surveys, we analysed events published in the Gaia Data Release 3 (Gaia DR3) microlensing catalogue. Here, we describe our selection of candidate dark lenses, where we suspect the lens is a white dwarf (WD), a neutron star (NS), a black hole (BH), or a mass-gap object, with a mass in the range between the heaviest NS and the least massive BH. We estimated the mass of the lenses using information obtained from the best-fitting microlensing models, source star, Galactic model, and the expected parameter distributions. We found eleven candidates for dark remnants: one WDs, three NSs, three mass-gap objects, and four BHs....

Aims. We carried out a project involving the systematic analysis of microlensing data from the Korea Microlensing Telescope Network survey. The aim of this project is to identify lensing events with complex anomaly features that are difficult to explain using standard binary-lens or binary-source models. Methods. Our investigation reveals that the light curves of microlensing events KMT-2021-BLG-0284, KMT-2022-BLG-2480, and KMT-2024-BLG-0412 display highly complex patterns with three or more anomaly features. These features cannot be adequately explained by a binary-lens (2L1S) model alone. However, the 2L1S model can effectively describe certain segments of the light curve. By incorporating an additional source into the modeling, we identified a comprehensive model that accounts for all the observed anomaly features. Results. Bayesian analysis, based on constraints provided by lensing observables, indicates that the lenses of KMT-2021-BLG-0284 and KMT-2024-BLG-0412 are binary systems composed of M dwarfs. For KMT-2022-BLG-2480, the primary lens is an early K-type main-sequence star with an M dwarf companion. The lenses of KMT-2021-BLG-0284 and KMT-2024-BLG-0412 are likely located in the bulge, whereas the lens of KMT-2022-BLG-2480 is more likely situated in the disk. In all events, the binary stars of the sources have similar magnitudes due to a detection bias favoring binary source events with a relatively bright secondary source star, which increases detection efficiency....

Aims. Building on previous works to construct a homogeneous sample of brown dwarfs in binary systems, we investigate microlensing events detected by the Korea Microlensing Telescope Network (KMTNet) survey during the 2022 and 2023 seasons. Methods. Given the difficulty in distinguishing brown-dwarf events from those produced by binary lenses with nearly equal-mass components, we analyze all lensing events detected during the seasons that exhibit anomalies characteristic of binary-lens systems. Results. Using the same criteria consistently applied in previous studies, we identify six additional brown dwarf candidates through the analysis of lensing events KMT-2022-BLG-0412, KMT-2022-BLG-2286, KMT-2023-BLG-0201, KMT-2023-BLG-0601, KMT-2023-BLG-1684, and KMT-2023-BLG-1743. An examination of the mass posteriors shows that the median mass of the lens companions ranges from 0.02 M_⊙ to 0.05 M_⊙, indicating that these companions fall within the brown-dwarf mass range. The mass of the primary lenses ranges from 0.11 M_⊙ to 0.68 M_⊙, indicating that they are low-mass stars with substantially lower masses compared to the Sun....

In the pursuit of understanding the population of stellar remnants within the Milky Way, we analyze the sample of ∼950 microlensing events observed by the Spitzer Space Telescope between 2014 and 2019. In this study we focus on a subsample of nine microlensing events, selected based on their long timescales, small microlensing parallaxes, and joint observations by the Gaia mission, to increase the probability that the chosen lenses are massive and the mass is measurable. Among the selected events we identify lensing black holes and neutron star candidates, with potential confirmation through forthcoming release of the Gaia time-series astrometry in 2026. Utilizing Bayesian analysis and Galactic models, along with the Gaia Data Release 3 proper-motion data, four good candidates for dark remnants were identified: OGLE-2016-BLG-0293, OGLE-2018-BLG-0483, OGLE-2018-BLG-0662, and OGLE-2015-BLG-0149, with lens masses of <inline-formula> <mml:math overflow="scroll"><mml:msubsup><mml:mrow><mml:mn>3.0</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>1.3</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>1.8</mml:mn></mml:mrow></mml:msubsup><mml:mspace width="0.25em"></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula>, <inline-formula> <mml:math overflow="scroll"><mml:msubsup><mml:mrow><mml:mn>4.7</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>2.1</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>3.2</mml:mn></mml:mrow></mml:msubsup><mml:mspace width="0.25em"></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula>, <inline-formula> <mml:math overflow="scroll"><mml:msubsup><mml:mrow><mml:mn>3.15</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.64</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.66</mml:mn></mml:mrow></mml:msubsup><mml:mspace width="0.25em"></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula> and <inline-formula> <mml:math overflow="scroll"><mml:msubsup><mml:mrow><mml:mn>1.40</mml:mn></mml:mrow><mml:mrow><mml:mo>‑</mml:mo><mml:mn>0.55</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo><mml:mn>0.75</mml:mn></mml:mrow></mml:msubsup><mml:mspace width="0.25em"></mml:mspace><mml:msub><mml:mrow><mml:mi>M</mml:mi></mml:mrow><mml:mrow><mml:mo>⊙</mml:mo></mml:mrow></mml:msub></mml:math> </inline-formula>, respectively. Notably, the first two candidates are expected to exhibit astrometric microlensing signals detectable by Gaia, offering the prospect of validating the lens masses. The methodologies developed in this work will be applied to the full Spitzer microlensing sample, populating and analyzing the timescale (t _E) versus parallax (π _E) diagram to derive constraints on the population of lenses in general and massive remnants in particular....

We present the analysis of the microlensing event OGLE-2015-BLG-0845, which was affected by both the microlensing parallax and xallarap effects. The former was detected via the simultaneous observations from the ground and Spitzer, and the latter was caused by the orbital motion of the source star in a relatively close binary. The combination of these two effects led to a mass measurement of the lens object, revealing a low-mass ($0.14 \pm 0.05 \, \mathrm{ M}_{\odot }$) M dwarf at the bulge distance ($7.6 \pm 1.0$ kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of $\sim 1.2$ and $\sim 0.9 \mathrm{ M}_{\odot }$, respectively, and the orbital period is $70 \pm 10$ d. OGLE-2015-BLG-0845 is the first single-lens event in which the lens mass is measured via the binarity of the source. Given the abundance of binary systems as potential microlensing sources, the xallarap effect may not be a rare phenomenon. Our work thus highlights the application of the xallarap effect in the mass determination of microlenses, and the same method can be used to identify isolated dark lenses....

<BR /> Aims: We investigated the nature of the anomalies appearing in four microlensing events KMT-2020-BLG-0757, KMT-2022-BLG-0732, KMT-2022-BLG-1787, and KMT-2022-BLG-1852. The light curves of these events commonly exhibit initial bumps followed by subsequent troughs that extend across a substantial portion of the light curves. <BR /> Methods: We performed thorough modeling of the anomalies to elucidate their characteristics. Despite their prolonged durations, which differ from the usual brief anomalies observed in typical planetary events, our analysis revealed that each anomaly in these events originated from a planetary companion located within the Einstein ring of the primary star. It was found that the initial bump arouse when the source star crossed one of the planetary caustics, while the subsequent trough feature occurred as the source traversed the region of minor image perturbations lying between the pair of planetary caustics. <BR /> Results: The estimated masses of the host and planet, their mass ratios, and the distance to the discovered planetary systems are (M_host/M_⊙, M_planet/M_J, q/10⁻³, D_L/kpc) = (0.58_−0.30^+0.33, 10.71_−5.61^+6.17, 17.61 ± 2.25, 6.67_−1.30^+0.93) for KMT-2020-BLG-0757, (0.53_−0.31^+0.31, 1.12_−0.65^+0.65, 2.01 ± 0.07, 6.66_−1.84^+1.19) for KMT-2022-BLG-0732, (0.42_−0.23^+0.32, 6.64_−3.64^+4.98, 15.07 ± 0.86, 7.55_−1.30^+0.89) for KMT-2022-BLG-1787, and (0.32_−0.19^+0.34, 4.98_−2.94^+5.42, 8.74 ± 0.49, 6.27_−1.15^+0.90) for KMT-2022-BLG-1852. These parameters indicate that all the planets are giants with masses exceeding the mass of Jupiter in our solar system and the hosts are low-mass stars with masses substantially less massive than the Sun....

<BR /> Aims: We aim to investigate the nature of the short-term anomaly that appears in the lensing light curve of KMT-2023-BLG-1866. The anomaly was only partly covered due to its short duration of less than a day, coupled with cloudy weather conditions and a restricted nighttime duration. <BR /> Methods: Considering the intricacy of interpreting partially covered signals, we thoroughly explored all potential degenerate solutions. Through this process, we identified three planetary scenarios that account for the observed anomaly equally well. These scenarios are characterized by the specific planetary parameters: (s, q)_inner = [0.9740 ± 0.0083, (2.46 ± 1.07) × 10⁻⁵], (s, q)_intermediate = [0.9779 ± 0.0017, (1.56 ± 0.25) × 10⁻⁵], and (s, q)_outer = [0.9894 ± 0.0107, (2.31 ± 1.29) × 10⁻⁵], where s and q denote the projected separation (scaled to the Einstein radius) and mass ratio between the planet and its host, respectively. We identify that the ambiguity between the inner and outer solutions stems from the inner-outer degeneracy, while the similarity between the intermediate solution and the others is due to an accidental degeneracy caused by incomplete anomaly coverage. <BR /> Results: Through Bayesian analysis utilizing the constraints derived from measured lensing observables and blending flux, our estimation indicates that the lens system comprises a very-low-mass planet orbiting an early M-type star situated approximately (6.2-6.5) kpc from Earth in terms of median posterior values for the different solutions. The median mass of the planet host is in the range of (0.48-0.51) M_⊙, and that of the planet's mass spans a range of (2.6-4.0) M_E, varying across different solutions. The detection of KMT-2023-BLG-1866Lb signifies the extension of the lensing surveys to very-low-mass planets that have been difficult to detect in earlier surveys....

<BR /> Aims: We undertake a project to reexamine microlensing data gathered from high-cadence surveys. The aim of the project is to reinvestigate lensing events whose light curves exhibit intricate anomaly features that are associated with caustics, but lack prior proposed models that would explain these features. <BR /> Methods: Through detailed reanalyses considering higher-order effects, we determined that it is vital to account for the orbital motions of lenses to accurately explain the anomaly features observed in the light curves of the lensing events OGLE-2018-BLG-0971, MOA-2023-BLG-065, and OGLE-2023-BLG-0136. <BR /> Results: We estimated the masses and distances to the lenses by conducting Bayesian analyses using the lensing parameters of the newly found lensing solutions. These analyses showed that the lenses of the events OGLE-2018-BLG-0971 and MOA-2023-BLG-065 are binaries composed of M dwarfs, while the lens of OGLE-2023-BLG-0136 likely is a binary composed of an early K-dwarf primary and a late M-dwarf companion. For all lensing events, the probability that the lens resides in the bulge is considerably higher than that it is located in the disk....

Following Shin et al. (2023b), which is a part of the "Systematic KMTNet Planetary Anomaly Search" series (i.e., a search for planets in the 2016 KMTNet prime fields), we conduct a systematic search of the 2016 KMTNet subprime fields using a semi-machine-based algorithm to identify hidden anomalous events missed by the conventional by-eye search. We find four new planets and seven planet candidates that were buried in the KMTNet archive. The new planets are OGLE-2016-BLG-1598Lb, OGLE-2016-BLG-1800Lb, MOA-2016-BLG-526Lb, and KMT-2016-BLG-2321Lb, which show typical properties of microlensing planets, i.e., giant planets orbit M-dwarf host stars beyond their snow lines. For the planet candidates, we find planet/binary or 2L1S/1L2S degeneracies, which are an obstacle to firmly claiming planet detections. By combining the results of Shin et al. (2023b) and this work, we find a total of nine hidden planets, which is about half the number of planets discovered by eye in 2016. With this work, we have met the goal of the systematic search series for 2016, which is to build a complete microlensing planet sample. We also show that our systematic searches significantly contribute to completing the planet sample, especially for planet/host mass ratios smaller than 10^‑3, which were incomplete in previous by-eye searches of the KMTNet archive....

The current studies of microlensing planets are limited by small number statistics. Follow-up observations of high-magnification microlensing events can efficiently form a statistical planetary sample. Since 2020, the Korea Microlensing Telescope Network (KMTNet) and the Las Cumbres Observatory (LCO) global network have been conducting a follow-up program for high-magnification KMTNet events. Here, we report the detection and analysis of a microlensing planetary event, KMT-2023-BLG-1431, for which the subtle (0.05 mag) and short-lived (5 hr) planetary signature was characterized by the follow-up from KMTNet and LCO. A binary-lens single-source (2L1S) analysis reveals a planet/host mass ratio of q = (0.72 ± 0.07) × 10^‑4, and the single-lens binary-source (1L2S) model is excluded by Δχ ² = 80. A Bayesian analysis using a Galactic model yields estimates of the host star mass of , the planetary mass of , and the lens distance of kpc. The projected planet-host separation of au or au, subject to the close/wide degeneracy. We also find that without the follow-up data, the survey-only data cannot break the degeneracy of central/resonant caustics and the degeneracy of 2L1S/1L2S models, showing the importance of follow-up observations for current microlensing surveys....

We present the analysis of the microlensing event OGLE-2014-BLG-0221, a planetary candidate event discovered in 2014. The photometric light curve is best described by a binary-lens single-source model. Our light-curve modeling finds two degenerate models, with event timescales of t _E ∼ 70 days and ∼110 days. These timescales are relatively long, indicating that the discovered system would possess a substantial mass. The two models are similar in their planetary parameters with a Jupiter mass ratio of q ∼ 10^‑3 and a separation of s ∼ 1.1. Bayesian inference is used to estimate the physical parameters of the lens, revealing that the shorter timescale model predicts 65% and 25% probabilities of a late-type star and white dwarf host, respectively, while the longer timescale model favors a black hole host with a probability ranging from 60% to 95%, under the assumption that stars and stellar remnants have equal probabilities of hosting companions with planetary mass ratios. If the lens is a remnant, this would be the second planet found by microlensing around a stellar remnant. The current separation between the source and lens stars is 41–139 mas depending on the models. This indicates the event is now ready for high-angular-resolution follow-up observations to rule out either of the models. If precise astrometric measurements are conducted in multiple bands, the centroid shift due to the color difference between the source and lens would be detected in the luminous lens scenario....

<BR /> Aims: We analyze the anomalies appearing in the light curves of the three microlensing events MOA-2022-BLG-563, KMT-2023-BLG-0469, and KMT-2023-BLG-0735. The anomalies exhibit common short-term dip features that appear near the peak. <BR /> Methods: From the detailed analyses of the light curves, we find that the anomalies were produced by planets accompanied by the lenses of the events. For all three events, the estimated mass ratios between the planet and host are on the order of 10⁻⁴: q ~ 8 × 10⁻⁴ for MOA-2022-BLG-563L, q ~ 2.5 × 10⁻⁴ for KMT-2023-BLG-0469L, and q ~ 1.9 × 10⁻⁴ for KMT-2023-BLG-0735L. The interpretations of the anomalies are subject to a common inner-outer degeneracy, which causes ambiguity when estimating the projected planet-host separation. <BR /> Results: We estimated the planet mass, M_p, host mass, M_h, and distance, D_L, to the planetary system by conducting Bayesian analyses using the observables of the events. The estimated physical parameters of the planetary systems are (M_h/M_⊙, M_p/M_J, D_L/kpc) = (0.48_−0.30^+0.36, 0.40_−0.25^+0.31, 6.53_−1.57^+1.12) for MOA-2022-BLG-563L, (0.47_−0.26^+0.35, 0.124_−0.067^+0.092, 7.07_−1.19^+1.03) for KMT-2023-BLG-0469L, and (0.62_−0.35^+0.34, 0.125_−0.070^+0.068, 6.26_−1.67^+1.27) for KMT-2023-BLG-0735L. According to the estimated parameters, all planets are cold planets with projected separations that are greater than the snow lines of the planetary systems, they have masses that lie between the masses of Uranus and Jupiter of the Solar System, and the hosts of the planets are main-sequence stars that are less massive than the Sun. In all cases, the planetary systems are more likely to be in the bulge with probabilities P_bulge = 64%, 73%, and 56% for MOA-2022-BLG-563, KMT-2023-BLG-0469, and KMT-2023-BLG-0735, respectively....

In this work, we update and develop algorithms for KMTNet tender-love care (TLC) photometry in order to create a new, mostly automated, TLC pipeline. We then start a project to systematically apply the new TLC pipeline to the historic KMTNet microlensing events, and search for buried planetary signals. We report the discovery of such a planet candidate in the microlensing event MOA-2019-BLG-421/KMT-2019-BLG-2991. The anomalous signal can be explained by either a planet around the lens star or the orbital motion of the source star. For the planetary interpretation, despite many degenerate solutions, the planet is most likely to be a Jovian planet orbiting an M or K dwarf, which is a typical microlensing planet. The discovery proves that the project can indeed increase the sensitivity of historic events and find previously undiscovered signals....

We investigate how the occurrence rate of giant planets (minimum mass &gt; 0.3 M _Jup) around Sun-like stars depends on the age, mass, and metallicity of their host stars. We develop a hierarchical Bayesian framework to infer the number of planets per star (NPPS) as a function of both planetary and stellar parameters. The framework fully takes into account the uncertainties in the latter by utilizing the posterior samples for the stellar parameters obtained by fitting stellar isochrone models to the spectroscopic parameters, Gaia DR3 parallaxes, and 2MASS K _s-band magnitudes adopting a certain bookkeeping prior. We apply the framework to 46 Doppler giants found around a sample of 382 Sun-like stars from the California Legacy Survey catalog that publishes spectroscopic parameters and search completeness for all the surveyed stars. We find evidence that the NPPS of hot Jupiters (orbital period P = 1-10 days) decreases roughly in the latter half of the main sequence over the timescale of ${ \mathcal O }(\mathrm{Gyr})$ , while that of cold Jupiters (P = 1-10 yr) does not. Assuming that this decrease is real and caused by tidal orbital decay, the modified stellar tidal quality factor ${Q}_{\star }^{ { \prime} }$ is implied to be ${ \mathcal O }({10}^{6})$ for a Sun-like main-sequence star orbited by a Jupiter-mass planet with P ≈ 3 days....

<BR /> Aims: We investigate the previous microlensing data collected by the KMTNet survey in search of anomalous events for which no precise interpretations of the anomalies had been suggested. From this investigation, we find that the anomaly in the lensing light curve of the event KMT-2021-BLG-1547 is approximately described by a binary-lens (2L1S) model with a lens possessing a giant planet, but the model leaves unexplained residuals. <BR /> Methods: We investigated the origin of the residuals by testing more sophisticated models that include either an extra lens component (3L1S model) or an extra source star (2L2S model) on top of the 2L1S configuration of the lens system. From these analyses, we find that the residuals from the 2L1S model originate from the existence of a faint companion to the source. The 2L2S solution substantially reduces the residuals and improves the model fit by Δχ² = 67.1 with respect to the 2L1S solution. The 3L1S solution also improves the fit, but its fit is worse than that of the 2L2S solution by Δχ² = 24.7. <BR /> Results: According to the 2L2S solution, the lens of the event is a planetary system with planet and host masses (M_p/M_J, M_h/M_⊙) = (1.47_−0.77^+0.64, 0.72_−0.38^+0.32) lying at a distance D_L = 5.07_−1.50^+0.98 kpc, and the source is a binary composed of a subgiant primary of a late G or an early K spectral type and a main-sequence companion of a K spectral type. The event demonstrates the need for sophisticated modeling of unexplained anomalies if one wants to construct a complete microlensing planet sample....

<BR /> Aims: As a part of the project aiming to build a homogeneous sample of binary-lens (2L1S) events containing brown dwarf (BD) companions, we investigate the 2021 season microlensing data collected by the Korea Microlensing Telescope Network (KMTNet) survey. <BR /> Methods: For this purpose, we first identified 2L1S events by conducting systematic analyses of anomalous lensing events. We then selected candidate BD companion events by applying the criterion that the mass ratio of the lens components is lower than q_th ∼ 0.1. <BR /> Results: From this procedure, we find four events including KMT-2021-BLG-0588, KMT-2021-BLG-1110, KMT-2021-BLG-1643, and KMT-2021-BLG-1770, for which the estimated mass ratios are q ∼ 0.10, 0.07, 0.08, and 0.15, respectively. Event KMT-2021-BLG-1770 was selected as a candidate even though the mass ratio is slightly greater than q_th because the lens mass expected from the measured short timescale of the event, t_E ∼ 7.6 days, is low. From the Bayesian analyses, we estimate that the primary and companion masses are (M₁/M_⊙,M₂/M_⊙) = (0.54_−0.24^+0.31, 0.053_−0.023^+0.031) for KMT-2021-BLG-0588L, (0.74_−0.35^+0.27, 0.055_−0.026^+0.020) for KMT-2021-BLG-1110L, (0.73_−0.17^+0.24,0.061_−0.014^+0.020) for KMT-2021-BLG-1643L, and (0.13_−0.07^+0.18, 0.020_−0.011^+0.028) for KMT-2021-BLG-1770L. It is estimated that the probabilities that the lens companions are in the BD mass range are 82%, 85%, 91%, and 59% for the individual events. To confirm the BD nature of the lens companions found in this and previous works by directly imaging the lenses from future high-resolution adaptive-optics (AO) followup observations, we provide the lens-source separations expected in 2030, which is the approximate year of the first AO light on 30 m class telescopes....

As a part of the "Systematic KMTNet Planetary Anomaly Search" series, we report five new planets (namely, OGLE-2016-BLG-1635Lb, MOA-2016-BLG-532Lb, KMT-2016-BLG-0625Lb, OGLE-2016-BLG-1850Lb, and KMT-2016-BLG-1751Lb) and one planet candidate (KMT-2016-BLG-1855), which were found by searching 2016 KMTNet prime fields. These buried planets show a wide range of masses from Earth-class to super-Jupiter-class and are located in both the disk and the bulge. The ultimate goal of this series is to build a complete planet sample. Because our work provides a complementary sample to other planet detection methods, which have different detection sensitivities, our complete sample will help us to obtain a better understanding of planet demographics in our Galaxy....

We report the discoveries of low-mass free-floating planet (FFP) candidates from the analysis of 2006-2014 MOA-II Galactic bulge survey data. In this data set, we found 6111 microlensing candidates and identified a statistical sample consisting of 3535 high-quality single-lens events with Einstein radius crossing times in the range 0.057 &lt; t _E/days &lt; 757, including 13 events that show clear finite-source effects with angular Einstein radii of 0.90 &lt; θ _E/μas &lt; 332.54. Two of the 12 events with t _E &lt; 1 day have significant finite-source effects, and one event, MOA-9y-5919, with t _E = 0.057 ± 0.016 days and θ _E = 0.90 ± 0.14 μas, is the second terrestrial-mass FFP candidate to date. A Bayesian analysis indicates a lens mass of ${0.75}_{-0.46}^{+1.23}$ M _⊕ for this event. The low detection efficiency for short-duration events implies a large population of low-mass FFPs. The microlensing detection efficiency for low-mass planet events depends on both the Einstein radius crossing times and the angular Einstein radii, so we have used image-level simulations to determine the detection efficiency dependence on both t _E and θ _E. This allows us to use a Galactic model to simulate the t _E and θ _E distribution of events produced by the known stellar populations and models of the FFP distribution that are fit to the data. Methods like this will be needed for the more precise FFP demographics determinations from Nancy Grace Roman Space Telescope data....

We present the first measurement of the mass function of free-floating planets (FFPs), or very wide orbit planets down to an Earth mass, from the MOA-II microlensing survey in 2006-2014. Six events are likely to be due to planets with Einstein radius crossing times t _E &lt; 0.5 days, and the shortest has t _E = 0.057 ± 0.016 days and an angular Einstein radius of θ _E = 0.90 ± 0.14 μas. We measure the detection efficiency depending on both t _E and θ _E with image-level simulations for the first time. These short events are well modeled by a power-law mass function, ${ { dN } }_{4}/d\mathrm{log}M={({2.18}_{-1.40}^{+0.52})\times (M/8\,{M}_{\oplus })}^{-{\alpha }_{4 } }$ dex^-1 star^-1 with ${\alpha }_{4}={0.96}_{-0.27}^{+0.47}$ for M/M _⊙ &lt; 0.02. This implies a total of $f={21}_{-13}^{+23}$ FFPs or very wide orbit planets of mass 0.33 &lt; M/M _⊕ &lt; 6660 per star, with a total mass of ${80}_{-47}^{+73}{M}_{\oplus }$ star^-1. The number of FFPs is ${19}_{-13}^{+23}$ times the number of planets in wide orbits (beyond the snow line), while the total masses are of the same order. This suggests that the FFPs have been ejected from bound planetary systems that may have had an initial mass function with a power-law index of α ~ 0.9, which would imply a total mass of ${171}_{-52}^{+80}{M}_{\oplus }$ star^-1. This model predicts that Roman Space Telescope will detect ${988}_{-566}^{+1848}$ FFPs with masses down to that of Mars (including ${575}_{-424}^{+1733}$ with 0.1 ≤ M/M _⊕ ≤ 1). The Sumi et al. large Jupiter-mass FFP population is excluded....

We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ ² values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q, and separation, s, cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ~ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters....

<BR /> Aims: We investigate the microlensing data collected in the 2022 season from high-cadence microlensing surveys in order to find weak signals produced by planetary companions to lenses. <BR /> Methods: From these searches, we find that two lensing events, KMT-2022-BLG-0475 and KMT-2022-BLG-1480, exhibit weak short-term anomalies. From a detailed modeling of the lensing light curves, we determine that the anomalies are produced by planetary companions with a mass ratio to the primary of q ~ 1.8 × 10⁻⁴ for KMT-2022-BLG-0475L and q ~ 4.3 × 10⁻⁴ for KMT-2022-BLG-1480L. <BR /> Results: We estimate that the host and planet masses and the projected planet-host separation are (M_h/M_⊙, M_p/M_U, a_⊥/au) = (0.43_−0.23^+0.35, 1.73_−0.92^+1.42, 2.03_−0.38^+0.25) for KMT-2022-BLG-0475L and (0.18_−0.09^+0.16, 1.82_−0.92^+1.60, 1.22_−0.14^+0.15) for KMT-2022-BLG-1480L, where M_U denotes the mass of Uranus. The two planetary systems have some characteristics in common: the primaries of the lenses are early-mid M dwarfs that lie in the Galactic bulge, and the companions are ice giants that lie beyond the snow lines of the planetary systems....

<BR /> Aims: We inspect the microlensing data of the KMTNet survey collected during the 2018-2020 seasons in order to find lensing events produced by binaries with brown dwarf (BD) companions. <BR /> Methods: In order to pick out binary-lens events with candidate BD lens companions, we conducted systematic analyses of all anomalous lensing events observed during the seasons from 2018 to 2020. By applying a selection criterion of mass ratio between the lens components of 0.03 ≲ q ≲ 0.1, we identify four binary-lens events with candidate BD companions, namely KMT-2018-BLG-0321, KMT-2018-BLG-0885, KMT-2019-BLG-0297, and KMT-2019-BLG-0335. For the individual events, we present interpretations of the lens systems and measure the observables that can be used to constrain the physical lens parameters. <BR /> Results: The masses of the lens companions estimated from the Bayesian analyses based on the measured observables indicate high probabilities that the lens companions are in the BD mass regime; that is, 59%, 68%, 66%, and 66% for the four respective events....

<BR /> Aims: Recently, there have been reports of various types of degeneracies in the interpretation of planetary signals induced by planetary caustics. In this work we check whether such degeneracies persist in the case of well-covered signals by analyzing the lensing event KMT-2021-BLG-1150, the light curve of which exhibits a densely and continuously covered short-term anomaly. <BR /> Methods: In order to identify degenerate solutions, we thoroughly investigated the parameter space by conducting dense grid searches for the lensing parameters. We then checked the severity of the degeneracy among the identified solutions. <BR /> Results: We identify a pair of planetary solutions resulting from the well-known inner-outer degeneracy, and find that interpreting the anomaly is not subject to any degeneracy other than the inner-outer degeneracy. The measured parameters of the planet separation (normalized to the Einstein radius) and mass ratio between the lens components are (s, q)_in ~ (1.297, 1.10 × 10⁻³) for the inner solution and (s, q)_out ~ (1.242, 1.15 × 10⁻³) for the outer solution. According to a Bayesian estimation, the lens is a planetary system consisting of a planet with a mass M_p = 0.88_−0.36^+0.38 M_j and its host with a mass M_h = 0.73_−0.30^+0.32 M_⊙ lying toward the Galactic center at a distance D_L = 3.8_−1.2^+1.3 kpc. By conducting analyses using mock data sets prepared to mimic those obtained with data gaps and under various observational cadences, we find that gaps in data can result in various degenerate solutions, while the observational cadence does not pose a serious degeneracy problem as long as the anomaly feature can be delineated....

We present the observations and analysis of a high-magnification microlensing planetary event, KMT-2022-BLG-0440, for which the weak and short-lived planetary signal was covered by both the KMTNet survey and follow-up observations. The binary-lens models with a central caustic provide the best fits, with a planet/host mass ratio, q = 0.75-1.00 × 10^-4 at 1σ. The binary-lens models with a resonant caustic and a brown-dwarf mass ratio are both excluded by Δχ² &gt; 70. The binary-source model can fit the anomaly well but is rejected by the 'colour argument' on the second source. From Bayesian analyses, it is estimated that the host star is likely a K or M dwarf located in the Galactic disc, the planet probably has a Neptune-mass, and the projected planet-host separation is $1.9^{+0.6}_{-0.7}$ or $4.6^{+1.4}_{-1.7}$ au, subject to the close/wide degeneracy. This is the third q &lt; 10^-4 planet from a high-magnification planetary signal (A ≳ 65). Together with another such planet, KMT-2021-BLG-0171Lb, the ongoing follow-up program for the KMTNet high-magnification events has demonstrated its ability to detect high-magnification planetary signals for q &lt; 10^-4 planets, which are challenging for the current microlensing surveys....

<BR /> Aims: We investigate the data collected by the high-cadence microlensing surveys during the 2022 season in search of planetary signals appearing in the light curves of microlensing events. From this search, we find that the lensing event MOA-2022-BLG-249 exhibits a brief positive anomaly that lasted for about one day, with a maximum deviation of ~0.2 mag from a single-source, single-lens model. <BR /> Methods: We analyzed the light curve under the two interpretations of the anomaly: one originated by a low-mass companion to the lens (planetary model) and the other originated by a faint companion to the source (binary-source model). <BR /> Results: We find that the anomaly is better explained by the planetary model than the binary-source model. We identified two solutions rooted in the inner-outer degeneracy and for both of them, the estimated planet-to-host mass ratio, q ~ 8 × 10⁻⁵, is very small. With the constraints provided by the microlens parallax and the lower limit on the Einstein radius, as well as the blend-flux constraint, we find that the lens is a planetary system, in which a super-Earth planet, with a mass of (4.83 ± 1.44) Μ_⊕, orbits a low-mass host star, with a mass of (0.18 ± 0.05) M_⊙, lying in the Galactic disk at a distance of (2.00 ± 0.42) kpc. The planet detection demonstrates the elevated microlensing sensitivity of the current high-cadence lensing surveys to low-mass planets....

We analyze the MOA-2020-BLG-208 gravitational microlensing event and present the discovery and characterization of a new planet, MOA-2020-BLG-208Lb, with an estimated sub-Saturn mass. With a mass ratio $q={3.17}_{-0.26}^{+0.28}\times {10}^{-4}$ , the planet lies near the peak of the mass-ratio function derived by the MOA collaboration and near the edge of expected sample sensitivity. For these estimates we provide results using two mass-law priors: one assuming that all stars have an equal planet-hosting probability, and the other assuming that planets are more likely to orbit around more massive stars. In the first scenario, we estimate that the lens system is likely to be a planet of mass ${m}_{\mathrm{planet } }={46}_{-24}^{+42}\,{M}_{\oplus }$ and a host star of mass ${M}_{\mathrm{host } }={0.43}_{-0.23}^{+0.39}\,{M}_{\odot }$ , located at a distance ${D}_{L}={7.49}_{-1.13}^{+0.99}\,\mathrm{kpc}$ . For the second scenario, we estimate ${m}_{\mathrm{planet } }={69}_{-34}^{+37}\,{M}_{\oplus }$ , ${M}_{\mathrm{host } }={0.66}_{-0.32}^{+0.35}\,{M}_{\odot }$ , and ${D}_{L}={7.81}_{-0.93}^{+0.93}\,\mathrm{kpc}$ . The planet has a projected separation as a fraction of the Einstein ring radius $s={1.3807}_{-0.0018}^{+0.0018}$ . As a cool sub-Saturn-mass planet, this planet adds to a growing collection of evidence for revised planetary formation models....

We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from a blind search of data gathered from Campaign 9 of the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is the first bound microlensing exoplanet discovered from space-based data. The event has caustic entry and exit points that are resolved in the K2C9 data, enabling the lens-source relative proper motion to be measured. We have fitted a binary microlens model to the Kepler data and to simultaneous observations from multiple ground-based surveys. Whilst the ground-based data only sparsely sample the binary caustic, they provide a clear detection of parallax that allows us to break completely the microlensing mass-position-velocity degeneracy and measure the planet's mass directly. We find a host mass of 0.58 ± 0.04 M_⊙ and a planetary mass of 1.1 ± 0.1 M_J. The system lies at a distance of 5.2 ± 0.2 kpc from Earth towards the Galactic bulge, more than twice the distance of the previous most distant planet found by Kepler. The sky-projected separation of the planet from its host is found to be 4.2 ± 0.3 au which, for circular orbits, deprojects to a host separation $a = 4.4^{+1.9}_{-0.4}$ au and orbital period $P = 13^{+9}_{-2}$ yr. This makes K2-2016-BLG-0005Lb a close Jupiter analogue orbiting a low-mass host star. According to current planet formation models, this system is very close to the host mass threshold below which Jupiters are not expected to form. Upcoming space-based exoplanet microlensing surveys by NASA's Nancy Grace Roman Space Telescope and, possibly, ESA's Euclid mission, will provide demanding tests of current planet formation models....

We present the analysis of three more planets from the KMTNet 2021 microlensing season. KMT-2021-BLG-0119Lb is a ~6M _Jup planet orbiting an early M dwarf or a K dwarf, KMT-2021-BLG-0192Lb is a ~2M _Nep planet orbiting an M dwarf, and KMT-2021-BLG-2294Lb is a ~1.25M _Nep planet orbiting a very-low-mass M dwarf or a brown dwarf. These by-eye planet detections provide an important comparison sample to the sample selected with the AnomalyFinder algorithm, and in particular, KMT-2021-BLG-2294 is a case of a planet detected by eye but not by algorithm. KMT-2021-BLG-2294Lb is part of a population of microlensing planets around very-low-mass host stars that spans the full range of planet masses, in contrast to the planet population at ≲0.1 au, which shows a strong preference for small planets....

In this paper, we describe the optical alignment method for the Prime-focus-Infrared Microlensing Experiment (PRIME) telescope which is a prime-focus near-infrared (NIR) telescope with a wide field of view for the microlensing planet survey toward the Galactic center that is the major task for the PRIME project. There are three steps for the optical alignment: preliminary alignment by a laser tracker, fine alignment by intra- and extra-focal (IFEF) image analysis technique, and complementary and fine alignment by the Hartmann test. We demonstrated that the first two steps work well by the test conducted in the laboratory in Japan. The telescope was installed at the Sutherland Observatory of South African Astronomical Observatory in August, 2022. At the final stage of the installation, we demonstrated that the third method works well and the optical system satisfies the operational requirement....

<BR /> Aims: With the aim of finding microlensing binaries containing brown dwarf (BD) companions, we investigate the microlensing survey data collected during the 2016-2018 seasons. <BR /> Methods: For this purpose, we first modeled lensing events with light curves exhibiting anomaly features that are likely to be produced by binary lenses. We then sorted out BD companion binary-lens events by applying the criterion that the companion-to-primary mass ratio is q ≲ 0.1. With this procedure, we identify six binaries with candidate BD companions: OGLE-2016-BLG-0890L, MOA-2017-BLG-477L, OGLE-2017-BLG-0614L, KMT-2018-BLG-0357L, OGLE-2018-BLG-1489L, and OGLE-2018-BLG-0360L. <BR /> Results: We estimated the masses of the binary companions by conducting Bayesian analyses using the observables of the individual lensing events. According to the Bayesian estimation of the lens masses, the probabilities for the lens companions of the events OGLE-2016-BLG-0890, OGLE-2017-BLG-0614, OGLE-2018-BLG-1489, and OGLE-2018-BLG-0360 to be in the BD mass regime are very high with P_BD &gt; 80%. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with P_BD = 61% and 69%, respectively....

Follow-up observations of high-magnification gravitational microlensing events can fully exploit their intrinsic sensitivity to detect extrasolar planets, especially those with small mass ratios. To make followup observations more uniform and efficient, we develop a system, HighMagFinder, to automatically alert possible ongoing high-magnification events based on the real-time data from the Korea Microlensing Telescope Network (KMTNet). We started a new phase of follow-up observations with the help of HighMagFinder in 2021. Here we report the discovery of two planets in high-magnification microlensing events, KMT-2021-BLG-0171 and KMT-2021-BLG-1689, which were identified by the HighMagFinder. We find that both events suffer the 'central-resonant' caustic degeneracy. The planet-host mass-ratio is q ~ 4.7 × 10^-5 or q ~ 2.2 × 10^-5 for KMT-2021-BLG-0171, and q ~ 2.5 × 10^-4 or q ~ 1.8 × 10^-4 for KMT-2021-BLG-1689. Together with two other events, four cases that suffer such degeneracy have been discovered in the 2021 season alone, indicating that the degenerate solutions may have been missed in some previous studies. We also propose a quantitative factor to weight the probability of each solution from the phase space. The resonant interpretations for the two events are disfavoured under this consideration. This factor can be included in future statistical studies to weight degenerate solutions....

We report on the observations, analysis and interpretation of the microlensing event MOA-2019-BLG-008. The observed anomaly in the photometric light curve is best described through a binary lens model. In this model, the source did not cross caustics and no finite-source effects were observed. Therefore, the angular Einstein ring radius θ _E cannot be measured from the light curve alone. However, the large event duration, t _E ~ 80 days, allows a precise measurement of the microlensing parallax π _E. In addition to the constraints on the angular radius θ _* and the apparent brightness I _s of the source, we employ the Besançon and GalMod galactic models to estimate the physical properties of the lens. We find excellent agreement between the predictions of the two galactic models: the companion is likely a resident of the brown dwarf desert with a mass M _p ~ 30 M _Jup, and the host is a main-sequence dwarf star. The lens lies along the line of sight to the Galactic bulge, at a distance of ≤4 kpc. We estimate that in about 10 yr the lens and source will be separated by ~55 mas, and it will be possible to confirm the exact nature of the lensing system by using high-resolution imaging from ground- or space-based observatories....