Browsing by Author "Skowron J"

Now showing 1 - 17 of 17
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    An analysis of binary microlensing event OGLE-2015-BLG-0060
    (Oxford University Press on behalf of the Royal Astronomical Society, 2019-08) Tsapras Y; Cassan A; Ranc C; Bachelet E; Street R; Udalski A; Hundertmark M; Bozza V; Beaulieu JP; Marquette JB; Euteneuer E; Bramich DM; Dominik M; Figuera Jaimes R; Horne K; Mao S; Menzies J; Schmidt R; Snodgrass C; Steele IA; Wambsganss J; Mróz P; Szymański MK; Soszyński I; Skowron J; Pietrukowicz P; Kozłowski S; Poleski R; Ulaczyk K; Pawlak M; Jørgensen UG; Skottfelt J; Popovas A; Ciceri S; Korhonen H; Kuffmeier M; Evans DF; Peixinho N; Hinse TC; Burgdorf MJ; Southworth J; Tronsgaard R; Kerins E; Andersen MI; Rahvar S; Wang Y; Wertz O; Rabus M; Calchi Novati S; D'Ago G; Scarpetta G; Mancini L; Abe F; Asakura Y; Bennett DP; Bhattacharya A; Donachie M; Evans P; Fukui A; Hirao Y; Itow Y; Kawasaki K; Koshimoto N; Li MCA; Ling CH; Masuda K; Matsubara Y; Muraki Y; Miyazaki S; Nagakane M; Ohnishi K; Rattenbury N; Saito T; Sharan A; Shibai H; Sullivan DJ; Sumi T; Suzuki D; Tristram PJ; Yamada T; Yonehara A; The RoboNet team; The OGLE collaboration; The MiNDSTEp collaboration; The MOA collaboration
    We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based on observations obtained from 13 different telescopes. Intensive coverage of the anomalous parts of the light curve was achieved by automated follow-up observations from the robotic telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of an anomalous microlensing event are well covered by follow-up data, allowing us to estimate the physical parameters of the lens. The strong detection of second-order effects in the event light curve necessitates the inclusion of longer-baseline survey data in order to constrain the parallax vector. We find that the event was most likely caused by a stellar binary-lens with masses M = 0.87 pm 0.12 mathrm{M} and M = 0.77 pm 0.11 mathrm{M}. The distance to the lensing system is 6.41 ± 0.14 kpc and the projected separation between the two components is 13.85 ± 0.16 au. Alternative interpretations are also considered.
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    An Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing
    (IOP Publishing, 2022-07-06) Lam CY; Lu JR; Udalski A; Bond I; Bennett DP; Skowron J; Mróz P; Poleski R; Sumi T; Szymański MK; Kozłowski S; Pietrukowicz P; Soszyński I; Ulaczyk K; Wyrzykowski Ł; Miyazaki S; Suzuki D; Koshimoto N; Rattenbury NJ; Hosek Jr MW; Abe F; Barry R; Bhattacharya A; Fukui A; Fujii H; Hirao Y; Itow Y; Kirikawa R; Kondo I; Matsubara Y; Matsumoto S; Muraki Y; Olmschenk G; Ranc C; Okamura A; Satoh Y; Silva SI; Toda T; Tristram PJ; Vandorou A; Yama H; Abrams NS; Agarwal S; Rose S; Terry SK
    We present the analysis of five black hole candidates identified from gravitational microlensing surveys. Hubble Space Telescope astrometric data and densely sampled light curves from ground-based microlensing surveys are fit with a single-source, single-lens microlensing model in order to measure the mass and luminosity of each lens and determine if it is a black hole. One of the five targets (OGLE-2011-BLG-0462/MOA-2011-BLG-191 or OB110462 for short) shows a significant >1 mas coherent astrometric shift, little to no lens flux, and has an inferred lens mass of 1.6-4.4 M . This makes OB110462 the first definitive discovery of a compact object through astrometric microlensing and it is most likely either a neutron star or a low-mass black hole. This compact-object lens is relatively nearby (0.70-1.92 kpc) and has a slow transverse motion of 30 km s-1. OB110462 shows significant tension between models well fit to photometry versus astrometry, making it currently difficult to distinguish between a neutron star and a black hole. Additional observations and modeling with more complex system geometries, such as binary sources, are needed to resolve the puzzling nature of this object. For the remaining four candidates, the lens masses are 2M , and they are unlikely to be black holes two of the four are likely white dwarfs or neutron stars. We compare the full sample of five candidates to theoretical expectations on the number of black holes in the Milky Way (1/4108) and find reasonable agreement given the small sample size.
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    An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing
    (IOP Publishing on behalf of the American Astronomical Society, 2022-07-06) Sahu KC; Anderson J; Casertano S; Bond HE; Udalski A; Dominik M; Calamida A; Bellini A; Brown TM; Rejkuba M; Bajaj V; Kains N; Ferguson HC; Fryer CL; Yock P; Mróz P; Kozłowski S; Pietrukowicz P; Poleski R; Skowron J; Soszyński I; Szymański MK; Ulaczyk K; Wyrzykowski Ł; Barry RK; Bennett DP; Bond IA; Hirao Y; Silva SI; Kondo I; Koshimoto N; Ranc C; Rattenbury NJ; Sumi T; Suzuki D; Tristram PJ; Vandorou A; Beaulieu J-P; Marquette J-B; Cole A; Fouqué P; Hill K; Dieters S; Coutures C; Dominis-Prester D; Bennett C; Bachelet E; Menzies J; Albrow M; Pollard K; Gould A; Yee JC; Allen W; Almeida LA; Christie G; Drummond J; Gal-Yam A; Gorbikov E; Jablonski F; Lee C-U; Maoz D; Manulis I; McCormick J; Natusch T; Pogge RW; Shvartzvald Y; Jørgensen UG; Alsubai KA; Andersen MI; Bozza V; Novati SC; Burgdorf M; Hinse TC; Hundertmark M; Husser T-O; Kerins E; Longa-Peña P; Mancini L; Penny M; Rahvar S; Ricci D; Sajadian S; Skottfelt J; Snodgrass C; Southworth J; Tregloan-Reed J; Wambsganss J; Wertz O; Tsapras Y; Street RA; Bramich DM; Horne K; Steele IA
    We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration (t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star's apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth's motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M ⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of �1/445 km s-1, suggesting that the BH received a "natal kick"from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.
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    Brown dwarf companions in microlensing binaries detected during the 2016-2018 seasons
    (EDP Sciences on behalf of the European Southern Observatory, 2022-11-08) Han C; Ryu Y-H; Shin I-G; Jung YK; Kim D; Hirao Y; Bozza V; Albrow MD; Zang W; Udalski A; Bond IA; Chung S-J; Gould A; Hwang K-H; Shvartzvald Y; Yang H; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Yee JC; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Silva SI; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Itow Y
    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 PBD > 80%. For MOA-2017-BLG-477 and KMT-2018-BLG-0357, the probabilities are relatively low with PBD = 61% and 69%, respectively.
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    Four sub-Jovian-mass planets detected by high-cadence microlensing surveys
    (EDP Sciences on behalf of the European Southern Observatory, 2022-08-05) Han C; Kim D; Gould A; Udalski A; Bond IA; Bozza V; Jung YK; Albrow MD; Chung S-J; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Zang W; Cha S-M; Kim D-J; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozaowski S; Ulaczyk K; Rybicki KA; Iwanek P; Abe F; Barry RK; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Itow Y; Kirikawa R; Koshimoto N; Kondo I; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Olmschenk G; Okamura A; Ranc C; Rattenbury NJ; Satoh Y; Silva SI; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H
    Aims. With the aim of finding short-term planetary signals, we investigated the data collected from current high-cadence microlensing surveys. Methods. From this investigation, we found four planetary systems with low planet-to-host mass ratios, including OGLE-2017-BLG-1691L, KMT-2021-BLG-0320L, KMT-2021-BLG-1303L, and KMT-2021-BLG-1554L. Despite the short durations, ranging from a few hours to a couple of days, the planetary signals were clearly detected by the combined data of the lensing surveys. We found that three of the planetary systems have mass ratios on the order of 10-4 and the other has a mass ratio that is slightly greater than 10-3. Results. The estimated masses indicate that all discovered planets have sub-Jovian masses. The planet masses of KMT-2021-BLG-0320Lb, KMT-2021-BLG-1303Lb, and KMT-2021-BLG-1554Lb correspond to ∼0.10, ∼0.38, and ∼0.12 times the mass of the Jupiter, and the mass of OGLE-2017-BLG-1691Lb corresponds to that of the Uranus. The estimated mass of the planet host KMT-2021-BLG-1554L, Mhost ∼ 0.08 M⊙, corresponds to the boundary between a star and a brown dwarf. Besides this system, the host stars of the other planetary systems are low-mass stars with masses in the range of ∼[0.3-0.6] M⊙. The discoveries of the planets fully demonstrate the capability of the current high-cadence microlensing surveys in detecting low-mass planets.
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    KMT-2019-BLG-1715: Planetary microlensing event with three lens masses and two source stars
    (IOP Publishing on behalf of the American Astronomical Society, 2021-06-01) Han C; Udalski A; Kim D; Jung YK; Lee C-U; Bond IA; Albrow MD; Chung S-J; Gould A; Hwang K-H; Kim H-W; Ryu Y-H; Shin I-G; Shvartzvald Y; Zang W; Yee JC; Cha S-M; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Kim C-H; Kim W-T; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki M; Abe F; Barry R; Bennett DP; Bhattacharya A; Donachie M; Fujii H; Fukui A; Itow Y; Hirao Y; Kirikawa R; Kondo I; Li MCA; Matsubara Y; Muraki Y; Miyazaki S; Ranc C; Rattenbury NJ; Satoh Y; Shoji H; Suematsu H; Sumi T; Suzuki D; Tanaka Y; Tristram PJ; Yamakawa T; Yamawaki T; Yonehara A
    We investigate the gravitational microlensing event KMT-2019-BLG-1715, the light curve of which shows two short-term anomalies from a caustic-crossing binary-lensing light curve: one with a large deviation and the other with a small deviation. We identify five pairs of solutions, in which the anomalies are explained by adding an extra lens or source component in addition to the base binary-lens model. We resolve the degeneracies by applying a method in which the measured flux ratio between the first and second source stars is compared with the flux ratio deduced from the ratio of the source radii. Applying this method leaves a single pair of viable solutions, in both of which the major anomaly is generated by a planetary-mass third body of the lens, and the minor anomaly is generated by a faint second source. A Bayesian analysis indicates that the lens comprises three masses: a planet-mass object with ∼2.6 MJ and binary stars of K and M dwarfs lying in the galactic disk. We point out the possibility that the lens is the blend, and this can be verified by conducting high-resolution follow-up imaging for the resolution of the lens from the source.
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    OGLE-2014-BLG-0221Lb: A Jupiter Mass Ratio Companion Orbiting Either a Late-type Star or a Stellar Remnant
    (American Astronomical Society, 2024-03-14) Kirikawa R; Sumi T; Bennett DP; Suzuki D; Koshimoto N; Miyazaki S; Bond IA; Udalski A; Rattenbury NJ; Abe F; Barry R; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Silva Ishitani S; Itow Y; Matsubara Y; Muraki Y; Olmschenk G; Ranc C; Satoh YK; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K; Mróz P; Poleski R; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski W; Ulaczyk K; Mróz MJ
    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
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    OGLE-2014-BLG-0319: A Sub-Jupiter-mass Planetary Event Encountered Degeneracy with Different Mass Ratios and Lens-source Relative Proper Motions
    (IOP Publishing on behalf of the American Astronomical Society, 2022-03-01) Miyazaki S; Suzuki D; Udalski A; Koshimoto N; Bennett DP; Sumi T; Rattenbury N; Cheongho H; Abe F; Barry RK; Bhattacharya A; Bond IA; Fukui A; Fujii H; Hirao Y; Silva SI; Itow Y; Kirikawa R; Kondo I; Munford B; Matsubara Y; Matsumoto S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Satoh YK; Toda T; Tristram PJ; Yama H; Yonehara A; Poleski R; Mróz P; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Wyrzykowski Ł
    We report the discovery of a sub-Jovian-mass planet, OGLE-2014-BLG-0319Lb. The characteristics of this planet will be added into a future extended statistical analysis of the Microlensing Observations in Astrophysics (MOA) collaboration. The planetary anomaly of the light curve is characterized by MOA and OGLE survey observations and results in three degenerate models with different planetary-mass ratios of q = (10.3, 6.6, 4.5) × 10-4. We find that the last two models require unreasonably small lens-source relative proper motions of μ rel ∼1 mas yr-1. Considering Galactic prior probabilities, we rule out these two models from the final result. We conduct a Bayesian analysis to estimate physical properties of the lens system using a Galactic model and find that the lens system is composed of a 0.49-0.27+0.35MJup sub-Jovian planet orbiting a 0.47-0.25+0.33M⊙ M dwarf near the Galactic Bulge. This analysis demonstrates that Galactic priors are useful to resolve this type of model degeneracy. This is important for estimating the mass-ratio function statistically. However, this method would be unlikely successful in shorter timescale events, which are mostly due to low-mass objects, like brown dwarfs or free-floating planets. Therefore, careful treatment is needed for estimating the mass-ratio function of the companions around such low-mass hosts, which only the microlensing can probe.
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    OGLE-2015-BLG-0845L: a low-mass M dwarf from the microlensing parallax and xallarap effects
    (Oxford University Press, 2024-09-01) Hu Z; Zhu W; Gould A; Udalski A; Sumi T; Chen P; Calchi Novati S; Yee JC; Beichman CA; Bryden G; Carey S; Fausnaugh M; Scott Gaudi B; Henderson CB; Shvartzvald Y; Wibking B; Mroz P; Skowron J; Poleski R; Szymanski MK; Soszynski I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki MG; Abe F; Barry R; Bennett DP; Bhattacharya A; Bond IA; Fujii H; Fukui A; Hamada R; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    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 ± 0.05 M) M dwarf at the bulge distance (7.6 ± 1.0 kpc). The source binary consists of a late F-type subgiant and a K-type dwarf of ∼ 1.2 and ∼ 0.9M, respectively, and the orbital period is 70 ± 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.
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    OGLE-2017-BLG-1049: Another giant planet microlensing event
    (Korean Astronomical Society, 2020-12-31) Kim YH; Chung S-J; Udalski A; Bond IA; Jung YK; Gould A; Albrow MD; Han C; Hwang K-H; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Zang W; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Poleski R; Mróz P; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Abe F; Barry R; Bennett DP; Bhattacharya A; Donachie M; Fujii H; Fukui A; Itow Y; Hirao Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Muraki Y; Miyazaki S; Ranc C; Rattenbury NJ; Satoh Y; Shoji H; Sumi T; Suzuki D; Tristram PJ; Tanaka Y; Yamawaki T; Yonehara A
    We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet–host star mass ratio of q = 9.53 ± 0.39 × 10−3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36−0.29M⊙ hosting a giant planet with Mp = 5.53+3.62 −2.87MJup, at a distance of DL = 5.67+1.11−1.52 kpc. The projected star–planet separation is a⊥ = 3.92+1.10−1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens–source proper motion is µrel ∼ 7 mas yr−1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.
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    OGLE-2018-BLG-0971, MOA-2023-BLG-065, and OGLE-2023-BLG-0136: Microlensing events with prominent orbital effects
    (EDP Sciences, 2024-06-14) Han C; Udalski A; Bond IA; Lee C-U; Gould A; Albrow MD; Chung S-J; Hwang K-H; Jung YK; Kim H-W; Ryu Y-H; Shvartzvald Y; Shin I-G; Yee JC; Yang H; Zang W; Cha S-M; Kim D; Kim D-J; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Rybicki KA; Iwanek P; Ulaczyk K; Wrona M; Gromadzki M; Mróz MJ; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    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.
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    OGLE-2019-BLG-0825: Constraints on the Source System and Effect on Binary-lens Parameters Arising from a Five-day Xallarap Effect in a Candidate Planetary Microlensing Event
    (American Astronomical Society, 2023-08-18) Satoh YK; Koshimoto N; Bennett DP; Sumi T; Rattenbury NJ; Suzuki D; Miyazaki S; Bond IA; Udalski A; Gould A; Bozza V; Dominik M; Hirao Y; Kondo I; Kirikawa R; Hamada R; Abe F; Barry R; Bhattacharya A; Fujii H; Fukui A; Fujita K; Ikeno T; Ishitani Silva S; Itow Y; Matsubara Y; Matsumoto S; Muraki Y; Niwa K; Okamura A; Olmschenk G; Ranc C; Toda T; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K; Mróz P; Poleski R; Skowron J; Szymański MK; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki M; Albrow MD; Chung S-J; Han C; Hwang K-H; Kim D; Jung YK; Kim HW; Ryu Y-H; Shin I-G; Shvartzvald Y; Yang H; Yee JC; Zang W; Cha S-M; Kim D-J; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Jørgensen UG; Longa-Peña P; Sajadian S; Skottfelt J; Snodgrass C; Tregloan-Reed J; Bach-Møller N; Burgdorf M; D'Ago G; Haikala L; Hitchcock J; Hundertmark M; Khalouei E; Peixinho N; Rahvar S; Southworth J; Spyratos P
    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.
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    Supplement: "an Isolated Mass-gap Black Hole or Neutron Star Detected with Astrometric Microlensing" (2022, ApJL, 933, L23)
    (IOP Publishing on behalf of the American Astronomical Society, 2022-07-06) Lam CY; Lu JR; Udalski A; Bond I; Bennett DP; Skowron J; Mróz P; Poleski R; Sumi T; Szymański MK; Kozłowski S; Pietrukowicz P; Soszyński I; Ulaczyk K; Wyrzykowski Ł; Miyazaki S; Suzuki D; Koshimoto N; Rattenbury NJ; Hosek Jr MW; Abe F; Barry R; Bhattacharya A; Fukui A; Fujii H; Hirao Y; Itow Y; Kirikawa R; Kondo I; Matsubara Y; Matsumoto S; Muraki Y; Olmschenk G; Ranc C; Okamura A; Satoh Y; Silva SI; Toda T; Tristram PJ; Vandorou A; Yama H; Abrams NS; Agarwal S; Rose S; Terry SK
    This supplement provides supporting material for Lam et al. We briefly summarize past gravitational microlensing searches for black holes (BHs) and present details of the observations, analysis, and modeling of five BH candidates observed with both ground-based photometric microlensing surveys and Hubble Space Telescope astrometry and photometry. We present detailed results for four of the five candidates that show no or low probability for the lens to be a BH. In these cases, the lens masses are <2 M ⊙, and two of the four are likely white dwarfs or neutron stars. We also present detailed methods for comparing the full sample of five candidates to theoretical expectations of the number of BHs in the Milky Way ( 1/4108).
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    Systematic KMTNet Planetary Anomaly Search. II. Six New q < 2 × 10−4 Mass-ratio Planets
    (IOP Publishing on behalf of the American Astronomical Society, 2022-02-01) Hwang K-H; Zang W; Gould A; Udalski A; Bond IA; Yang H; Mao S; Albrow MD; Chung S-J; Han C; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge R; Mróz P; Poleski R; Skowron J; Szymański MK; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Gromadzki M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Munford B; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh YK; Shoji H; Silva SI; Sumi T; Suzuki D; Tristram PJ; Yonehara A; Zhang X; Zhu W; Penny MT; Fouqué P
    We apply the automated AnomalyFinder algorithm of Paper I to 2018-2019 light curves from the ≃13 deg2 covered by the six KMTNet prime fields, with cadences Γ ≥ 2 hr-1. We find a total of 11 planets with mass ratios q < 2 × 10-4, including 6 newly discovered planets, 1 planet that was reported in Paper I, and recovery of 4 previously discovered planets. One of the new planets, OGLE-2018-BLG-0977Lb, is in a planetary caustic event, while the other five (OGLE-2018-BLG-0506Lb, OGLE-2018-BLG-0516Lb, OGLE-2019-BLG-1492Lb, KMT-2019-BLG-0253, and KMT-2019-BLG-0953) are revealed by a "dip"in the light curve as the source crosses the host-planet axis on the opposite side of the planet. These subtle signals were missed in previous by-eye searches. The planet-host separations (scaled to the Einstein radius), s, and planet-host mass ratios, q, are, respectively, (s, q × 105) = (0.88, 4.1), (0.96 ± 0.10, 8.3), (0.94 ± 0.07, 13), (0.97 ± 0.07, 18), (0.97 ± 0.04, 4.1), and (0.74, 18), where the "± "indicates a discrete degeneracy. The 11 planets are spread out over the range . Together with the two planets previously reported with q ∼ 10-5 from the 2018-2019 nonprime KMT fields, this result suggests that planets toward the bottom of this mass-ratio range may be more common than previously believed.
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    Systematic KMTNet Planetary Anomaly Search. IX. Complete Sample of 2016 Prime-field Planets
    (American Astronomical Society, 2023-08-14) Shin I-G; Yee JC; Zang W; Yang H; Hwang K-H; Han C; Gould A; Udalski A; Bond IA; Albrow MD; Chung S-J; Jung YK; Ryu Y-H; Shvartzvald Y; Cha S-M; Kim D-J; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Rybicki KA; Iwanek P; Ulaczyk K; Wrona M; Gromadzki M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hamada R; Hirao Y; Ishitani Silva S; Itow Y; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    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.
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    Systematic KMTNet Planetary Anomaly Search. XI. Complete Sample of 2016 Subprime Field Planets
    (American Astronomical Society, 2024-06-03) Shin I-G; Yee JC; Zang W; Han C; Yang H; Gould A; Lee C-U; Udalski A; Sumi T; Albrow MD; Chung S-J; Hwang K-H; Jung YK; Ryu Y-H; Shvartzvald Y; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymański MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Rybicki KA; Iwanek P; Ulaczyk K; Wrona M; Gromadzki M; Abe F; Bando K; Barry R; Bennett DP; Bhattacharya A; Bond IA; Fujii H; Fukui A; Hamada R; Hamada S; Hamasaki N; Hirao Y; Silva SI; Itow Y; Kirikawa R; Koshimoto N; Matsubara Y; Miyazaki S; Muraki Y; Nagai T; Nunota K; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Suzuki D; Tomoyoshi M; Tristram PJ; Vandorou A; Yama H; Yamashita K
    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.
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    Systematic KMTNet planetary anomaly search: V. Complete sample of 2018 prime-field
    (EDP Sciences, 2022-08-08) Gould A; Han C; Zang W; Yang H; Hwang K-H; Udalski A; Bond IA; Albrow MD; Chung S-J; Jung YK; Ryu Y-H; Shin I-G; Shvartzvald Y; Yee JC; Cha S-M; Kim D-J; Kim H-W; Kim S-L; Lee C-U; Lee D-J; Lee Y; Park B-G; Pogge RW; Mróz P; Szymanski MK; Skowron J; Poleski R; Soszyński I; Pietrukowicz P; Kozłowski S; Ulaczyk K; Rybicki KA; Iwanek P; Wrona M; Abe F; Barry R; Bennett DP; Bhattacharya A; Fujii H; Fukui A; Hirao Y; Silva SI; Kirikawa R; Kondo I; Koshimoto N; Matsubara Y; Matsumoto S; Miyazaki S; Muraki Y; Okamura A; Olmschenk G; Ranc C; Rattenbury NJ; Satoh Y; Sumi T; Suzuki D; Toda T; Tristram PJ; Vandorou A; Yama H; Beichman C; Bryden G; Novati SC; Gaudi BS; Henderson CB; Penny MT; Jacklin S; Stassun KG
    We complete the analysis of all 2018 prime-field microlensing planets identified by the Korea Microlensing Telescope Network (KMTNet) Anomaly Finder. Among the ten previously unpublished events with clear planetary solutions, eight are either unambiguously planetary or are very likely to be planetary in nature: OGLE-2018-BLG-1126, KMT-2018-BLG-2004, OGLE-2018-BLG-1647, OGLE-2018-BLG-1367, OGLE-2018-BLG-1544, OGLE-2018-BLG-0932, OGLE-2018-BLG-1212, and KMT-2018-BLG-2718. Combined with the four previously published new Anomaly Finder events and 12 previously published (or in preparation) planets that were discovered by eye, this makes a total of 24 2018 prime-field planets discovered or recovered by Anomaly Finder. Together with a paper in preparation on 2018 subprime planets, this work lays the basis for the first statistical analysis of the planet mass-ratio function based on planets identified in KMTNet data. By systematically applying the heuristic analysis to each event, we identified the small modification in their formalism that is needed to unify the so-called close-wide and inner-outer degeneracies.