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Context.TheVera RubinObservatory will provide an unprecedented set of time-dependent observations of the sky. The planned Legacy Survey of Space and Time (LSST), operating for ten years, will provide dense light curves for thousands of active galactic nuclei (AGN) in deep drilling fields (DDFs) and less dense light curves for millions of AGN from the main survey (MS). Aims.We model the prospects for measuring the time delays for the AGN emission lines with respect to the continuum, using these data. Methods.We modeled the artificial light curves using the Timmer-König algorithm. We used the exemplary cadence to sample them (one for the MS and one for the DDF), we supplement light curves with the expected contamination by the strong emission lines (Hβ, Mg II, and CIV, as well as with Fe II pseudo-continuum and the starlight). We chose suitable photometric bands that are appropriate for the redshift and compared the assumed line time-delay with the recovered time delay for 100 statistical realizations of the light curves. Results.We show that time delays for emission lines can be well measured from the main survey for the bright tail of the quasar distribution (about 15% of all sources) with an accuracy within 1σerror. For the DDF, the results for fainter quasars are also reliable when the entire ten years of data are used. There are also some prospects to measure the time delays for the faintest quasars at the lowest redshifts from the first two years of data, and possibly even from the first season. The entire quasar population will allow us to obtain results of apparently high accuracy, but in our simulations, we see a systematic offset between the assumed and recovered time delay that depends on the redshift and source luminosity. This offset will not disappear even in the case of large statistics. This problem might affect the slope of the radius-luminosity relation and cosmological applications of quasars if no simulations are performed that correct for these effects. 

Aims. Light curves of microlensing events occasionally deviate from the smooth and symmetric form of a single-lens single-source event. While most of these anomalous events can be accounted for by employing a binary-lens single-source (2L 1S) or a single-lens binary-source (1L2S) framework, it is established that a small fraction of events remain unexplained by either of these interpretations. We carried out a project in which data collected by high-cadence microlensing surveys were reinvestigated with the aim of uncovering the nature of anomalous lensing events with no proposed 2L 1S or 1L 2S models. Methods. From the project we found that the anomaly appearing in the lensing event OGLE-2023-BLG-0836 cannot be explained by the usual interpretations, and we conducted a comprehensive analysis of the event. From thorough modeling of the light curve under sophisticated lens-system configurations, we arrived at the conclusion that a triple-mass lens system is imperative to account for the anomalous features observed in the lensing light curve. Results. From the Bayesian analysis using the measured observables of the event timescale and angular Einstein radius, we determined that the least massive component of the lens has a planetary mass of 4.36_−2.18^+2.35M_J. This planet orbits within a stellar binary system composed of two stars with masses 0.71_−0.36^+0.38M_⊙and 0.56_−0.28^+0.30M_⊙. This lensing event signifies the sixth occurrence of a planetary microlensing system in which a planet belongs to a stellar binary system. 

Abstract We report the analysis of four unambiguous planets and one possible planet from the subprime fields (Γ ≤ 1 hr⁻¹) of the 2017 Korea Microlensing Telescope Network (KMTNet) microlensing survey, to complete the KMTNet AnomalyFinder planetary sample for the 2017 subprime fields. They are KMT-2017-BLG-0849, KMT-2017-BLG-1057, OGLE-2017-BLG-0364, and KMT-2017-BLG-2331 (unambiguous), as well as KMT-2017-BLG-0958 (possible). For the four unambiguous planets, the mean planet–host mass ratios,q, are (1.0, 1.2, 4.6, 13) × 10⁻⁴, the median planetary masses are (6.4, 24, 76, 171)M_⊕, and the median host masses are (0.19, 0.57, 0.49, 0.40)M_⊙, respectively, found from a Bayesian analysis. We have completed the Anomaly Finder planetary sample from the first 4 yr of KMTNet data (2016–2019), with 112 unambiguous planets in total, which nearly tripled the microlensing planetary sample. The “sub-Saturn desert” ( $\log q=\left(-3.6,-3.0\right)$) found in the 2018 and 2019 KMTNet samples is confirmed by the 2016 and 2017 KMTNet samples. 

Aims. We investigate the 2023 season data from high-cadence microlensing surveys with the aim of detecting partially covered shortterm signals and revealing their underlying astrophysical origins. Through this analysis, we ascertain that the signals observed in the lensing events KMT-2023-BLG-0416, KMT-2023-BLG-1454, and KMT-2023-BLG-1642 are of planetary origin. Methods. Considering the potential degeneracy caused by the partial coverage of signals, we thoroughly investigate the lensing-parameter plane. In the case of KMT-2023-BLG-0416, we have identified two solution sets, one with a planet-to-host mass ratio ofq~ 10⁻²and the other withq~ 6 × 10⁻⁵, within each of which there are two local solutions emerging due to the inner-outer degeneracy. For KMT-2023-BLG-1454, we discern four local solutions featuring mass ratios ofq~ (1.7−4.3) × 10⁻³. When it comes to KMT-2023-BLG-1642, we identified two locals withq~ (6 − 10) × 10⁻³resulting from the inner-outer degeneracy. Results. We estimate the physical lens parameters by conducting Bayesian analyses based on the event time scale and Einstein radius. For KMT-2023-BLG-0416L, the host mass is ~0.6M_⊙, and the planet mass is ~(6.1−6.7)M_Jaccording to one set of solutions and ~0.04M_Jaccording to the other set of solutions. KMT-2023-BLG-1454Lb has a mass roughly half that of Jupiter, while KMT-2023-BLG-1646Lb has a mass in the range of between 1.1 to 1.3 times that of Jupiter, classifying them both as giant planets orbiting mid M-dwarf host stars with masses ranging from 0.13 to 0.17 solar masses. 

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. 

Abstract We complete the analysis of planetary candidates found by the KMT AnomalyFinder for the 2017 prime fields that cover ∼13 deg². We report three unambiguous planets: OGLE-2017-BLG-0640, OGLE-2017-BLG-1275, and OGLE-2017-BLG-1237. The first two of these were not previously identified, while the last was not previously published due to technical complications induced by a nearby variable. We further report that a fourth anomalous event, the previously recognized OGLE-2017-BLG-1777, is very likely to be planetary, although its light curve requires unusually complex modeling because the lens and source both have orbiting companions. One of the three unambiguous planets, OGLE-2017-BLG-1275, is the first AnomalyFinder discovery that has a Spitzer microlens parallax measurement,π_E≃ 0.045 ± 0.015, implying that this planetary system almost certainly lies in the Galactic bulge. In the order listed, the four planetary events have planet-host mass ratiosqand normalized projected separationssof $(\log q,s)=(-2.31,0.61)$, (−2.06, 0.63/1.09), (−2.10, 1.04), and (−2.86, 0.72). Combined with previously published events, the 2017 prime fields contain 11 unambiguous planets with well-measuredqand one very likely candidate, of which three are AnomalyFinder discoveries. In addition to these 12, there are three other unambiguous planets with large uncertainties inq. 

Abstract 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 ${3.0}_{-1.3}^{+1.8}{M}_{\odot }$, ${4.7}_{-2.1}^{+3.2}{M}_{\odot }$, ${3.15}_{-0.64}^{+0.66}{M}_{\odot }$and ${1.40}_{-0.55}^{+0.75}{M}_{\odot }$, 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. 

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. 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], wheresandqdenote 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. 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. 

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. 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. 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. 

Abstract The gravitational microlensing technique is most sensitive to planets in a Jupiter-like orbit and has detected more than 200 planets. However, only a few wide-orbit (s> 2) microlensing planets have been discovered, wheresis the planet-to-host separation normalized to the angular Einstein ring radius,θ_E. Here, we present the discovery and analysis of a strong candidate wide-orbit microlensing planet in the event OGLE-2017-BLG-0448. The whole light curve exhibits long-term residuals to the static binary-lens single-source model, so we investigate the residuals by adding the microlensing parallax, microlensing xallarap, an additional lens, or an additional source. For the first time, we observe a complex degeneracy between all four effects. The wide-orbit models withs∼ 2.5 and a planet-to-host mass ratio ofq∼ 10⁻⁴are significantly preferred, but we cannot rule out the close models withs∼ 0.35 andq∼ 10⁻³. A Bayesian analysis based on a Galactic model indicates that, despite the complicated degeneracy, the surviving wide-orbit models all contain a super-Earth-mass to Neptune-mass planet at a projected planet-host separation of ∼6 au and the surviving close-orbit models all consist of a Jovian-mass planet at ∼1 au. The host star is probably an M or K dwarf. We discuss the implications of this dimension-degeneracy disaster on microlensing light-curve analysis and its potential impact on statistical studies.