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.

The DECam Rogue Earths and Mars Survey (DREAMS), a NOIRLab survey program, has been conducting a three-year survey covering a 5 deg^2 area in the Galactic bulge since 2025 June. Its primary science goal is to detect low-mass free-floating planets through microlensing, while its minute-level cadence also enables the detection and characterization of rapid phenomena on timescales of minutes to hours such as stellar flares and pulsating stars. Here, we present the data reduction and calibration of the DREAMS observations obtained in 2025 and introduce the first DREAMS data release (DR1). DR1 includes 1,856 z-band observations and 325 r-band observations for 59,372,789 stars. The DREAMS DR1 catalog contains at least twice as many stars as any previous catalog covering the same 5 deg^2 area. We present DREAMS light curves for a known blue large-amplitude pulsator and a known transiting system to demonstrate the survey's capabilities. We also perform a pilot search for short-duration variables over about 0.4

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 not bound 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 and 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 3000 simulated events. Assuming the A. Cassan et al. 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.

We report the discovery of Gaia23bra b, the first gravitationally bound microlensing planet detected by the Transiting Exoplanet Survey Satellite (TESS). Initially flagged as a single-lens event by the Gaia Science Alerts system, Gaia23bra was serendipitously observed by TESS over two consecutive sectors. During those TESS sectors, the light curve of the event displayed caustic-crossing features characteristic of a binary-lens event. The joint modeling of Gaia and TESS photometry with pyLIMA, supplemented by stellar parameter inference using pyLIMASS, suggests a K dwarf ( ML=0.79-0.17+0.19M circle dot ) hosting a Jovian planet with MP=1.63-0.38+0.42MJup at a projected separation of a perpendicular to,min approximate to 4.8au . This result underscores the synergy between high-cadence photometry and long-baseline monitoring for robust microlensing characterization. Its location along the Galactic Plane highlights TESS's unexpected capacity for microlensing science through its all-sky coverage and its potential to detect planets in regions beyond the Galactic Bulge.

The Vera C. Rubin Legacy Survey of Space and Time will discover thousands of microlensing events across the Milky Way Galaxy, allowing for the study of populations of exoplanets, stars, and compact objects. It will reach deeper limiting magnitudes over a wider area than any previous survey. We evaluate numerous survey strategies simulated in the Rubin Operation Simulations (OpSims) to assess the discovery and characterization efficiencies of microlensing events. We have implemented three metrics in the Rubin Metric Analysis Framework: a discovery metric and two characterization metrics, where one estimates how well the lightcurve is covered and the other quantifies how precisely event parameters can be determined. We also assess the characterizability of microlensing parallax, critical for detection of free-floating black hole lenses, in a representative bulge and disk field. We find that, given Rubin's baseline cadence, the discovery and characterization efficiency will be higher for longer duration and larger parallax events. Microlensing discovery efficiency is dominated by observing footprint, where more time spent looking at regions of high stellar density including the Galactic bulge, Galactic plane, and Magellanic clouds, leads to higher discovery and characterization rates. However, if the observations are stretched over too wide an area, including low-priority areas of the Galactic plane with fewer stars and higher extinction, event characterization suffers by > 10%, which could impact exoplanet, binary star, and compact object events alike. We find that some rolling strategies (where Rubin focuses on a fraction of the sky in alternating years) in the Galactic bulge can lead to a 15-20% decrease in microlensing parallax characterization, so rolling strategies should be chosen carefully to minimize losses.

The Nancy Grace Roman Space Telescope (Roman) will unveil for the first time the full architecture of planetary systems across Galactic distances through the discovery of up to 200,000 cool and hot exoplanets using microlensing and transit detection methods. Roman's huge exoplanet haul, and Galactic reach, will require new methods to leverage the full exoplanet demographic content of the combined microlensing and transit samples, given the different sensitivity bias of the techniques to planet and host properties and Galactic location. We present a framework for technique-agnostic exoplanet demography (TAED) that can allow large, multi-technique exoplanet samples distributed over Galactic distance scales to be combined for demographic studies. Our TAED forward modelling and retrieval framework uses parameterised model exoplanet demographic distributions to embed planetary systems within a stellar population synthesis model of the Galaxy, enabling internally consistent forecasts to be made for all detection methods that are based on spatio-kinematic system properties. In this paper, as a first test of the TAED framework, we apply it to simulated transit datasets based on the Kepler Data Release 25 to assess parameter recovery accuracy and method scalability for a single large homogeneous dataset. We find that optimisation using differential evolution provides a computationally scalable framework that gives a good balance between computational efficiency and accuracy of parameter recovery.

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, Mh = 0.025+(0.050)-M-0.012(circle dot), accompanied by an Earth-mass planet with Mc = 1.9+(3.9)-M-1.0(circle plus).

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

We present the analysis of OGLE-2014-BLG-1760, a planetary system in the galactic bulge. We combine Keck Adaptive Optics follow-up observations in K -band with re-reduced light-curve data to confirm the source and lens star identifications and stellar types. The re-reduced Microlensing Observations in Astrophysics data set had an important impact on the light-curve model. We find the Einstein ring crossing time of the event to be ∼2.5 days shorter than previous fits, which increases the planetary mass-ratio and decreases the source angular size by a factor of 0.25. Our OSIRIS images obtained 6 yr after the peak of the event show a source-lens separation of 54.20 ± 0.23 mas, which leads to a relative proper motion of μ _rel = 9.14 ± 0.05 mas yr ^−1 and is larger than the previous light-curve-only models. Our analysis shows that the event consists of a Jupiter-mass planet of M _p = 0.931 ± 0.117 M _Jup orbiting a K-dwarf star of M _* = 0.803 ± 0.097 M _⊙ with a K -magnitude of K _L = 18.30 ± 0.05, located in the galactic bulge or bar. We also attempt to constrain the source properties using the source angular size θ _* and K -magnitude. Our results favor the scenario of the source being a younger star in the galactic disk, behind the galactic bulge, but future multicolor observations are needed to constrain the source and thus the lens properties.

Context. Identifying black holes is essential for our understanding of the development of stars and can reveal novel principles of physics. Gravitational microlensing provides an exceptional opportunity to examine an undetectable population of black holes in the Milky Way. In particular, long-lasting events are likely to be associated with massive lenses, including black holes. Aims. We present an analysis of the Gaia18ajz microlensing event reported by the Gaia Science Alerts system. Gaia18ajz is a long-timescale event exhibiting features indicative of the annual microlensing parallax effect. Our objective is to estimate its lens parameters based on the best-fitting model. Methods. We used photometric data obtained from the Gaia satellite and terrestrial observatories to investigate a variety of microlensing models and calculate the most probable mass and distance to the lens, taking into consideration a Galactic model as a prior. Subsequently, we applied a mass-brightness relation to evaluate the likelihood that the lens is a main sequence star. We also describe the DarkLensCode (DLC), an open- source routine that computes the distribution of probable lens mass, distance, and luminosity employing the Galaxy priors on stellar density and velocity for microlensing events with detected microlensing parallax. Results. We modelled the Gaia18ajz event and found its two possible models, the most probable Einstein timescales for which are 316(+36) (-30) days and 299(+25) (-22) days. Applying Galaxy priors for stellar density and motion, we calculated a most probable lens mass of 4.9(-2.3)(+5.4) M (R) located at 1.14(+0.75) (-0.57) kpc, and a less probably mass of 11.1(+10.3) (-4.7) M (R) located at 1.31(-0.60)(+0.80) kpc. Our analysis of the blended light suggests that the lens is likely a dark remnant of stellar evolution rather than a main sequence star.

The Nancy Grace Roman Space Telescope will expand the reach of gravitational microlensing surveys by increasing the number of events monitored and the precision of their light curves. We investigate Roman's ability to detect triple-lens microlensing systems, cases where a foreground star with two bound exoplanets produces detectable anomalies in a microlensing event, using its planned high-cadence observations toward the Galactic bulge. We simulate a large set of high-magnification microlensing light curves based on Roman's expected survey characteristics. A detection criterion, based on a required χ^2 improvement for a two-planet model, is applied to determine whether the second planet can be reliably distinguished from a single-planet (binary-lens) model. Our simulations show that the majority of two-planet microlensing events would be detectable with Roman. Events in which both planets are relatively massive (planet-star mass ratios of order 10^-3), or in which the more massive planet occupies a favorable resonant configuration, produce strong central perturbations, resulting in detection efficiencies of roughly 90%. By contrast, systems with only low-mass planets (q ∼ 10^-4) or with less favorable alignments generate much weaker signals, which often fall below the detection threshold. In general, the planetary mass ratios and the resulting caustic geometry (e.g., central caustic size in resonant versus wide/close orbits) are the dominant factors governing detectability. Taking into account the expected frequency of planetary systems and the fraction of high-magnification events, we estimate that Roman will detect a high-magnification triple-lens event in approximately 4.5% of multi-planet microlensing events, corresponding to about 64 events over the course of the full survey.

Context. Gravitational microlensing is a method that is used to discover planet-hosting systems at distances of several kiloparsec in the Galactic disk and bulge. We present the analysis of a microlensing event reported by the Gaia photometric alert team that might have a bright lens. Aims. In order to infer the mass and distance to the lensing system, the parallax measurement at the position of Gaia21blx was used. In this particular case, the source and the lens have comparable magnitudes and we cannot attribute the parallax measured by Gaia to the lens or source alone. Methods. Since the blending flux is important, we assumed that the Gaia parallax is the flux-weighted average of the parallaxes of the lens and source. Combining this assumption with the information from the microlensing models and the finite source effects we were able to resolve all degeneracies and thus obtained the mass, distance, luminosities and projected kinematics of the binary lens and the source. Results. According to the best model, the lens is a binary system at 2.18 ± 0.07 kpc from Earth. It is composed of a G star with 0.95± 0.17 M_⊙ and a K star with 0.53 ± 0.07 M_⊙. The source is likely to be an F subgiant star at 2.38 ± 1.71 kpc with a mass of 1.10 ± 0.18 M_⊙. Both lenses and the source follow the kinematics of the thin-disk population. We also discuss alternative models, that are disfavored by the data or by prior expectations, however.

Nancy Grace Roman Space Telescope will revolutionize our understanding of the Galactic Bulge with its Galactic Bulge Time Domain survey. At the same time, Rubin Observatories's Legacy Survey of Space and Time (LSST) will monitor billions of stars in the Milky Way. The proposed Roman survey of the Galactic Plane, with its NIR passbands and exquisite spacial resolution, promises groundbreaking insights for a wide range of time-domain galactic astrophysics. In this white paper, we describe the scientific returns possible from the combination of the Roman Galactic Plane Survey with the data from LSST.

The Robotic Observations of Microlensing Events/Reactive Event Assessment Survey was a Key Project at Las Cumbres Observatory (hereafter LCO) which continuously monitored 20 selected fields (3.76 sq.deg) in the Galactic Bulge throughout their seasonal visibility window over a three-year period, between 2017 March and 2020 March. Observations were made in three optical passbands (SDSS-g ', -r ', -i '), and LCO's multi-site telescope network enabled the survey to achieve a typical cadence of similar to 10 hr in i ' and similar to 15 hr in g ' and r ' . In addition, intervals of higher cadence (<1 hr) data were obtained during monitoring of key microlensing events within the fields. This paper describes the Difference Image Analysis data reduction pipeline developed to process these data, and the process for combining the photometry from LCO's three observing sites in the Southern Hemisphere. The full timeseries photometry for all similar to 8 million stars, down to a limiting magnitude of i similar to 18 mag is provided in the data release accompanying this paper, and samples of the data are presented for exemplar microlensing events, illustrating how the tri-band data are used to derive constraints on the microlensing source star parameters, a necessary step in determining the physical properties of the lensing object. The timeseries data also enables a wealth of additional science, for example in characterizing long-timescale stellar variability, and a few examples of the data for known variables are presented.

We present pyLIMASS, a novel algorithm for estimating the physical properties of the lensing system in microlensing events. The main idea of pyLIMASS is to combine all available information regarding the microlensing event, defined as observables , and to estimate the parameter distributions of the system, such as the lens mass and distance. The algorithm is based on isochrones for the stars model and combines the observables using a Gaussian mixture approach. After describing the mathematical formalism and its implementation, we discuss the algorithm’s performance on simulated and published events. Generally, the pyLIMASS estimations are in good agreement (i.e., within 1 σ ) with the results of the selected published events, making it an effective tool to estimate the lens properties and their distribution. The applicability of the method was tested by using a catalog of realistically simulated events that could be observed by the future Galactic Bulge Time Domain Survey of the Nancy Grace Roman Space Telescope. By solely using constraints from the Roman lightcurves and images, pyLIMASS estimates the masses of the lens of the Roman catalog with a median precision of 20% with almost no bias.

As the Kepler mission has done for hot exoplanets, the ESA Euclid and NASA Roman missions have the potential to create a breakthrough in our understanding of the demographics of cool exoplanets, including planets on very wide orbits, unbound, or "free-floating", planets (FFPs). Current ground-based microlensing observations have provided preliminary evidence for a potentially significant population of Super-Earth FFPs. Roman will dedicate part of its core survey program to the detection of cool exoplanets via microlensing, while Euclid may undertake a microlensing program as an ancillary science goal. We argue that simultaneous observations of short-duration microlensing events by Roman and Euclid will enable not just the verification of FFPs, but also a direct measurement of their masses, distances and transverse motions, via the detection of microlens parallax between Euclid and Roman. We use simulations of the joint-mission detection capabilities to show that parallax detections will be possible down to Earth-mass FFPs. The mass and phase-space measurements from a joint survey could thus provide strong clues to the primary mode of FFP formation. We also demonstrate that an early brief Euclid survey (∼5 h) of the Roman fields shortly after the Euclid launch would be also very valuable. It would allow the measurement of at least 10% of the events’ relative proper motions and 35% of the lens magnitudes very early on the life of the Roman Survey. We further discuss additional valuable science that will be facilitated by a joint Roman-Euclid microlensing campaign.

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. 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. Results. The estimated masses of the host and planet, their mass ratios, and the distance to the discovered planetary systems are (M-host/M-circle dot, 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.

We present an analysis of high angular resolution images of the microlensing target MOA-2007-BLG-192 using Keck adaptive optics and the Hubble Space Telescope. The planetary host star is robustly detected as it separates from the background source star in nearly all of the Keck and Hubble data. The amplitude and direction of the lens-source separation allows us to break a degeneracy related to the microlensing parallax and source radius crossing time. Thus, we are able to reduce the number of possible solutions by a factor of ${\sim}2$, demonstrating the power of high angular resolution follow-up imaging for events with sparse light curve coverage. Following Bennett et al. 2023, we apply constraints from the high resolution imaging on the light curve modeling to find host star and planet masses of $M_{\textrm{host}} = 0.28 \pm 0.04M_{\odot}$ and $m_p = 12.49^{+65.47}_{-8.03}M_{\oplus}$ at a distance from Earth of $D_L = 2.16 \pm 0.30\,$kpc. This work illustrates the necessity for the Nancy Grace Roman Galactic Exoplanet Survey (RGES) to use its own high resolution imaging to inform light curve modeling for microlensing planets that the mission discovers.

We report discovering an exoplanet from following up a microlensing event alerted by Gaia. The event Gaia22dkv is toward a nearby disk source at ~2.5 kpc rather than the traditional bulge microlensing fields. Our primary analysis yields a Jovian planet with M_p = 0.50 +/- 0.05 M_J at a projected orbital separation r_perp = 1.63 +/- 0.17 AU. The host is a turnoff star with mass 1.24 +/- 0.06 M_sun and distance of 1.35 +/- 0.09 kpc, and at r'~14, it is far brighter than any previously discovered microlensing planet host, opening up the opportunity of testing the microlensing model with radial velocity (RV) observations. RV data can be used to measure the planet's orbital period and eccentricity, and they also enable searching for inner planets of the microlensing cold Jupiter, as expected from the "inner-outer correlation" inferred from Kepler and RV discoveries. Furthermore, we show that Gaia astrometric microlensing will not only allow precise measurements of its angular Einstein radius theta_E, but also directly measure the microlens parallax vector and unambiguously break a geometric light-curve degeneracy, leading to definitive characterization of the lens system.

During the last 25 yr, hundreds of binary stars and planets have been discovered toward the Galactic bulge by microlensing surveys. Thanks to a new generation of large-sky surveys, it is now possible to regularly detect microlensing events across the entire sky. The OMEGA Key Projet at the Las Cumbres Observatory carries out automated follow-up observations of microlensing events alerted by these surveys with the aim of identifying and characterizing exoplanets as well as stellar remnants. In this study, we present the analysis of the binary lens event Gaia20bof. By automatically requesting additional observations, the OMEGA Key Project obtained dense time coverage of an anomaly near the peak of the event, allowing characterization of the lensing system. The observed anomaly in the lightcurve is due to a binary lens. However, several models can explain the observations. Spectroscopic observations indicate that the source is located at ≤2.0 kpc, in agreement with the parallax measurements from Gaia. While the models are currently degenerate, future observations, especially the Gaia astrometric time series as well as high-resolution imaging, will provide extra constraints to distinguish between them.