Year: 2025
Type: article
Abstract: Aims. In single-lens microlensing events, the event timescale (tE) is typically the only measurable parameter that constrains the lens mass. Since tE scales with the square root of the lens mass (tE ∝ M1/2), a short duration may suggest a low-mass lens, such as a brown dwarf (BD). However, a short tE can also result from a high relative proper motion between the lens and the source, making it difficult to uniquely identify BD candidates based on timescale alone. In contrast, binary-lens events often allow for the measurement of the angular Einstein radius (θE) in addition to tE. When both tE and θE are small, the likelihood that the lens is of low mass increases significantly. In this study, we analyze microlensing events observed between 2023 and 2024 to identify cases likely caused by binary systems composed of BDs. Methods. Applying the criteria of well-resolved caustics, short timescales (tE ≲ 9 days), and small angular Einstein radii (θE ≲ 0.17 mas), we identified six candidate binary BD events: MOA-2023-BLG-331, KMT-2023-BLG-2019, KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486. Analysis of these events leads to models that provide precise estimates for both lensing observables, tE and θE. Results. We estimated the masses of the binary components through Bayesian analysis, utilizing the constraints from tE and θE. The results show that for the events KMT-2024-BLG-1005, KMT-2024-BLG-1518, MOA-2024-BLG-181, and KMT-2024-BLG-2486, the probability that both binary components lie within the BD mass range exceeds 50%, indicating a high likelihood that the lenses of these events are binary BDs. In contrast, for MOA-2023-BLG-331L and KMT-2023-BLG-2019L, the probabilities that the lower-mass components of the binary lenses lie within the BD mass range exceed 50%, while the probabilities for the heavier components are below 50%, suggesting that these systems are more likely to consist of a low-mass M dwarf and a BD. The BD nature of the binary candidates can ultimately be confirmed by combining the measured lens-source relative proper motions with high-resolution imaging taken at a later time.
Authors: Cheongho Han, Chung-Uk Lee, Ian A. Bond, Andrzej Udalski, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, Youn Kil Jung, Kyu-Ha Hwang, Yoon-Hyun Ryu, Yossi Shvartzvald, In-Gu Shin, Jennifer C. Yee, Weicheng Zang, Hongjing Yang, Sang-Mok Cha, Doeon Kim, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge, Przemek Mróz, Michał K. Szymański, Jan Skowron, Radosław Poleski, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof A. Rybicki, Patryk Iwanek, Krzysztof Ulaczyk, Marcin Wrona, Mariusz Gromadzki, Mateusz J. Mróz, Michał Jaroszyński, Marcin Kiraga, Fumio Abe, David P. Bennett, Aparna Bhattacharya, Akihiko Fukui, Ryusei Hamada, Stela Ishitani Silva, Yuki Hirao, Asahi Idei, Shota Miyazaki, Yasushi Muraki, Tutumi Nagai, Kansuke Nunota, Greg Olmschenk, Clément Ranc, Nicholas J. Rattenbury, Yuki Satoh, Takahiro Sumi, Daisuke Suzuki, Takuto Tamaoki, Sean K. Terry, Paul J. Tristram, Aikaterini Vandorou, Hibiki Yama
Institutions: Chungbuk National University, Korea Astronomy and Space Science Institute, Massey University, University of Warsaw, University of Canterbury, The Ohio State University, Weizmann Institute of Science, Center for Astrophysics Harvard & Smithsonian, Tsinghua University, Kyung Hee University, University of Warwick, Villanova University, Nagoya University, Goddard Space Flight Center, University of Maryland, College Park, Instituto de Astrofísica de Canarias, The University of Tokyo, The University of Osaka, Catholic University of America, Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Centre National de la Recherche Scientifique, Institut d'Astrophysique de Paris, Sorbonne Université, University of Auckland, Kanto Gakuin University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Science Foundation, Smithsonian Institution, Alexander von Humboldt-Stiftung, Korea Astronomy and Space Science Institute, Ministry of Science and ICT, South Korea, Korea Research Environment Open Network, Smithsonian Astrophysical Observatory, Japan Society for the Promotion of Science
Awards: 重力マイクロレンズを用いた地球質量の系外惑星、浮遊惑星及びブラックホールの探査, NSF-BSF: The Frequency and Mass-Ratio Distribution of Super-Earths in KMTNet, G4207453364, 近赤外線重力マイクロレンズ観測による冷たい系外惑星・浮遊惑星の形成過程の解明, Search for cold exoplanets and free-floating planets by near infrared gravitational microlensing observation, G8411355473
OpenAlex ID: W7114788965
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