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Aims. We systematically inspected the microlensing data acquired by the KMTNet survey during the previous seasons in order to find anomalous lensing events for which the anomalies in the lensing light curves cannot be explained by the usual binary-lens or binary-source interpretations. Methods. From the inspection, we find that interpreting the three lensing events OGLE-2018-BLG-0584, KMT-2018-BLG-2119, and KMT-2021-BLG-1122 requires four-body (lens+source) models, in which either both the lens and source are binaries (2L2S event) or the lens is a triple system (3L1S event). Following the analyses of the 2L2S events presented in our previous work, here we present the 3L1S analysis of the KMT-2021-BLG-1122. Results. It is found that the lens of the event KMT-2021-BLG-1122 is composed of three masses, in which the projected separations (normalized to the angular Einstein radius) and mass ratios between the lens companions and the primary are ( s 2 ,  q 2 )∼(1.4, 0.53) and ( s 3 ,  q 3 )∼(1.6, 0.24). By conducting a Bayesian analysis, we estimate that the masses of the individual lens components are ( M 1 ,  M 2 ,  M 3 )∼(0.47  M ⊙ , 0.24  M ⊙ , 0.11  M ⊙ ). The companions are separated in projection from the primary by ( a ⊥, 2 ,  a ⊥, 3 )∼(3.5, 4.0) AU. The lens of KMT-2018-BLG-2119 is the first triple stellar system detected via microlensing. 

Aims. We inspect the four microlensing events KMT-2021-BLG-1968, KMT-2021-BLG-2010, KMT-2022-BLG-0371, and KMT-2022-BLG-1013, for which the light curves exhibit partially covered short-term central anomalies. We conduct detailed analyses of the events with the aim of revealing the nature of the anomalies. Methods. We tested various models that can explain the anomalies of the individual events, including the binary-lens (2L1S) and binary-source (1L2S) interpretations. Under the 2L1S interpretation, we thoroughly inspected the parameter space to determine the existence of degenerate solutions, and if they existed, we tested whether the degeneracy could be resolved. Results. We find that the anomalies in KMT-2021-BLG-2010 and KMT-2022-BLG-1013 are uniquely defined by planetary-lens interpretations with planet-to-host mass ratios of q ~ 2.8 × 10 −3 and ~1.6 × 10 −3 , respectively. For KMT-2022-BLG-0371, a planetary solution with a mass ratio q ~ 4 × 10 −4 is strongly favored over the other three degenerate 2L1S solutions with different mass ratios based on the χ 2 and relative proper motion arguments, and a 1L2S solution is clearly ruled out. For KMT-2021-BLG-1968, on the other hand, we find that the anomaly can be explained either by a planetary or a binary-source interpretation, making it difficult to firmly identify the nature of the anomaly. From the Bayesian analyses of the identified planetary events, we estimate that the masses of the planet and host are ( M p / M J , M h / M ⊙ ) = (1.07 −0.68 +1.15 , 0.37 −0.23 +0.40 ), (0.26 −0.11 +0.13 , 0.63 −0.28 +0.32 ), and (0.31 −0.16 +0.46 , 0.18 −0.10 +0.28 ) for KMT-2021-BLG-2010L, KMT-2022-BLG-0371L, and KMT-2022-BLG-1013L, respectively. 

Aims. We investigate the microlensing data collected during the 2017–2019 seasons in the peripheral Galactic bulge fields with the aim of finding planetary signals in microlensing light curves observed with relatively sparse coverage. Methods. We first sort out lensing events with weak short-term anomalies in the lensing light curves from the visual inspection of all non-prime-field events, and then test various interpretations of the anomalies. From this procedure, we find two previously unidentified candidate planetary lensing events KMT-2017-BLG-0673 and KMT-2019-BLG-0414. It is found that the planetary signal of KMT-2017-BLG-0673 was produced by the source crossing over a planet-induced caustic, but it was previously missed because of the sparse coverage of the signal. On the other hand, the possibly planetary signal of KMT-2019-BLG-0414 was generated without caustic crossing, and it was previously missed due to the weakness of the signal. We identify a unique planetary solution for KMT-2017-BLG-0673. However, for KMT-2019-BLG-0414, we identify two pairs of planetary solutions, for each of which there are two solutions caused by the close-wide degeneracy, and a slightly less favored binary-source solution, in which a single lens mass gravitationally magnified a rapidly orbiting binary source with a faint companion (xallarap). Results. From Bayesian analyses, it is estimated that the planet KMT-2017-BLG-0673Lb has a mass of 3.7 −2.1 +2.2 M J , and it is orbiting a late K-type host star with a mass of 0.63 −0.35 +0.37 M ⊙ . Under the planetary interpretation of KMT-2010-BLG-0414L, a star with a mass of 0.74 −0.38 +0.43 M ⊙ hosts a planet with a mass of ~3.2–3.6 M J depending on the solution. We discuss the possible resolution of the planet-xallarap degeneracy of KMT-2019-BLG-0414 by future adaptive-optics observations on 30 m class telescopes. The detections of the planets indicate the need for thorough investigations of non-prime-field lensing events for the complete census of microlensing planet samples. 

Aims. The light curve of the microlensing event KMT-2021-BLG-0240 exhibits a short-lasting anomaly with complex features near the peak at the 0.1 mag level from a single-lens single-source model. We conducted modeling of the lensing light curve under various interpretations to reveal the nature of the anomaly. Methods. It is found that the anomaly cannot be explained with the usual model based on a binary-lens (2L1S) or a binary-source (1L2S) interpretation. However, a 2L1S model with a planet companion can describe part of the anomaly, suggesting that the anomaly may be deformed by a tertiary lens component or a close companion to the source. From the additional modeling, we find that all the features of the anomaly can be explained with either a triple-lens (3L1S) model or a binary-lens binary-source (2L2S) model. However, it is difficult to validate the 2L2S model because the light curve does not exhibit signatures induced by the source orbital motion and the ellipsoidal variations expected by the close separation between the source stars according to the model. We, therefore, conclude that the two interpretations cannot be distinguished with the available data, and either can be correct. Results. According to the 3L1S solution, the lens is a planetary system with two sub-Jovian-mass planets in which the planets have masses of 0.32–0.47 M J and 0.44–0.93 M J , and they orbit an M dwarf host. According to the 2L2S solution, on the other hand, the lens is a single planet system with a mass of ~0.21 M J orbiting a late K-dwarf host, and the source is a binary composed of a primary of a subgiant or a turnoff star and a secondary of a late G dwarf. The distance to the planetary system varies depending on the solution: ~7.0 kpc according to the 3L1S solution and ~6.6 kpc according to the 2L2S solution. 

Aims. We conducted a systematic investigation of the microlensing data collected during the previous observation seasons for the purpose of re-analyzing anomalous lensing events with no suggested plausible models. Methods. We found that two anomalous lensing events, OGLE-2018-BLG-0584 and KMT-2018-BLG-2119, cannot be explained with the usual models based on either a binary-lens single-source (2L1S) or a single-lens binary-source (1L2S) interpretation. We tested the feasibility of explaining the light curves of the events with more sophisticated models by adding either an extra lens (3L1S model) or a source (2L2S model) component to the 2L1S lens system configuration. Results. We find that a 2L2S interpretation explains the light curves of both events well and that for each event there are a pair of solutions resulting from the close and wide degeneracy. For the event OGLE-2018-BLG-0584, the source is a binary composed of two K-type stars and the lens is a binary composed of two M dwarfs. For KMT-2018-BLG-2119, the source is a binary composed of two dwarfs of G and K spectral types and the lens is a binary composed of a low-mass M dwarf and a brown dwarf. 

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. 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). 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. 

Aims. The light curve of the microlensing event KMT-2021-BLG-1898 exhibits a short-term central anomaly with double-bump features that cannot be explained by the usual binary-lens or binary-source interpretations. With the aim of interpreting the anomaly, we analyze the lensing light curve under various sophisticated models. Methods. We find that the anomaly is explained by a model, in which both the lens and source are binaries (2L2S model). For this interpretation, the lens is a planetary system with a planet/host mass ratio of q ~ 1.5 × 10 −3 , and the source is a binary composed of a turn off or a subgiant star and a mid K dwarf. The double-bump feature of the anomaly can also be depicted by a triple-lens model (3L1S model), in which the lens is a planetary system containing two planets. Among the two interpretations, the 2L2S model is favored over the 3L1S model not only because it yields a better fit to the data, by ∆ χ 2 = [14.3−18.5], but also the Einstein radii derived independently from the two stars of the binary source result in consistent values. According to the 2L2S interpretation, KMT-2021-BLG-1898 is the third planetary lensing event occurring on a binary stellar system, following MOA-2010-BLG-117 and KMT-2018-BLG-1743. Results. Under the 2L2S interpretation, we identify two solutions resulting from the close-wide degeneracy in determining the planet-host separation. From a Bayesian analysis, we estimate that the planet has a mass of ~0.7−0.8 M J , and it orbits an early M dwarf host with a mass of ~0.5 M ⊙ . The projected planet-host separation is ~1.9 AU and ~3.0 AU according to the close and wide solutions, respectively. 

Aims. We reexamine high-magnification microlensing events in the previous data collected by the KMTNet survey with the aim of finding planetary signals that were not noticed before. In this work, we report the planetary system KMT-2018-BLG-1988L, which was found from this investigation. Methods. The planetary signal appears as a deviation with ≲0.2 mag from a single-lens light curve and lasted for about 6 h. The deviation exhibits a pattern of a dip surrounded by weak bumps on both sides of the dip. The analysis of the lensing light curve indicates that the signal is produced by a low-mass-ratio ( q ~ 4 × 10 −5 ) planetary companion located near the Einstein ring of the host star. Results. The mass of the planet, M planet  = 6.8 −3.5 +4.7  M ⊕ and 5.6 −2.8 +3.8  M ⊕ for the two possible solutions, estimated from the Bayesian analysis indicates that the planet is in the regime of a super-Earth. The host of the planet is a disk star with a mass of M host  = 0.47 −0.25 +0.33  M ⊙ and a distance of D L  = 4.2 −.14 +1.8 kpc. KMT-2018-BLG-1988Lb is the 18th known microlensing planet with a mass below the upper limit of a super-Earth. The fact that 15 out of the 18 known microlensing planets with masses ≲10  M ⊕ were detected in the 5 yr following the full operation of the KMTNet survey indicates that the KMTNet database is an important reservoir of very low-mass planets. 

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. 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. 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  > 80%. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with P BD  = 61% and 69%, respectively. 

Aims. The high-magnification microlensing event KMT-2021-BLG-1077 exhibits a subtle and complex anomaly pattern in the region around the peak. We analyze the lensing light curve of the event with the aim of revealing the nature of the anomaly. Methods. We test various models in combination with several interpretations: that the lens is a binary (2L1S), the source is a binary (1L2S), both the lens and source are binaries (2L2S), or the lens is a triple system (3L1S). We search for the best-fit models under the individual interpretations of the lens and source systems. Results. We find that the anomaly cannot be explained by the usual three-body (2L1S and 1L2S) models. The 2L2S model improves the fit compared to the three-body models, but it still leaves noticeable residuals. On the other hand, the 3L1S interpretation yields a model explaining all the major anomalous features in the lensing light curve. According to the 3L1S interpretation, the estimated mass ratios of the lens companions to the primary are ~1.56 × 10 −3 and ~1.75 × 10 −3 , which correspond to ~1.6 and ~1.8 times the Jupiter/Sun mass ratio, respectively, and therefore the lens is a multiplanetary system containing two giant planets. With the constraints of the event time-scale and angular Einstein radius, it is found that the host of the lens system is a low-mass star of mid-to-late M spectral type with amass of M h = 0.14 −0.07 +0.19 M Θ , and it hosts two gas giant planets with masses of M p1 = 0.22 −0.12 +0.31 M J and M p2 = 0.25 −0.13 +0.35 . The planets lie beyond the snow line of the host with projected separations of a ⊥,p1 = 1.26 −1.08 +1.41 AU and a ⊥,p2 = 0.93 −0.80 +1.05 AU. The planetary system resides in the Galactic bulge at a distance of D L = 8.24 −1.16 +1.02 kpc. The lens of the event is the fifth confirmed multiplanetary system detected by microlensing following OGLE-2006-BLG-109L, OGLE-2012-BLG-0026L, OGLE-2018-BLG-1011L, and OGLE-2019-BLG-0468L.