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Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii

Han, Cheongho and Lee, Chung-Uk and Udalski, Andrzej and Gould, Andrew and Bond, Ian A. and Bozza, Valerio and Albrow, Michael D. and Chung, Sun-Ju and Hwang, Kyu-Ha and Jung, Youn Kil and Ryu, Yoon-Hyun and Shin, In-Gu and Shvartzvald, Yossi and Yee, Jennifer C. and Zang, Weicheng and Cha, Sang-Mok and Kim, Dong-Jin and Kim, Hyoun-Woo and Kim, Seung-Lee and Lee, Dong-Joo and Lee, Yongseok and Park, Byeong-Gon and Pogge, Richard W. and Jee, M. James and Kim, Doeon and Mróz, Przemek and Szymański, Michał K. and Skowron, Jan and Poleski, Radek and Soszyński, Igor and Pietrukowicz, Paweł and Kozłowski, Szymon and Ulaczyk, Krzysztof and Rybicki, Krzysztof A. and Iwanek, Patryk and Wrona, Marcin and Abe, Fumio and Barry, Richard and Bennett, David P. and Bhattacharya, Aparna and Donachie, Martin and Fujii, Hirosane and Fukui, Akihiko and Itow, Yoshitaka and Hirao, Yuki and Kamei, Yuhei and Kondo, Iona and Koshimoto, Naoki and Li, Man Cheung Alex and Matsubara, Yutaka and Muraki, Yasushi and Miyazaki, Shota and Nagakane, Masayuki and Ranc, Clément and Rattenbury, Nicholas J. and Satoh, Yuki and Shoji, Hikaru and Suematsu, Haruno and Sullivan, Denis J. and Sumi, Takahiro and Suzuki, Daisuke and Tristram, Paul J. and Yamakawa, Takeharu and Yamawaki, Tsubasa and Yonehara, Atsunori (2020) Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii. Astronomical Journal, 159 (4). Art. No. 134. ISSN 1538-3881.

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Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales t_E because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales (t_E ≲ 6 days) but also with very small angular Einstein radii (θ_E ≲ 0.05 mas) among the events that have been found in the 2016–2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Monte Carlo simulations of Galactic events conducted with the combined t_E and θ_E constraint, it is estimated that the lens masses of the individual events are 0.051^(+0.100)_(−0.027) M⊙, 0.044^(+0.090)_(−0.023) M⊙, and 0.046^(+0.067)_(−0.023) M⊙/0.038^(+0.056)_(−0.019) M⊙ and the probability of the lens mass smaller than the lower limit of stars is ~80% for all events. We point out that routine lens mass measurements of short-timescale lensing events require survey-mode space-based observations.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Han, Cheongho0000-0002-2641-9964
Bozza, Valerio0000-0003-4590-0136
Chung, Sun-Ju0000-0001-6285-4528
Hwang, Kyu-Ha0000-0002-9241-4117
Ryu, Yoon-Hyun0000-0001-9823-2907
Shin, In-Gu0000-0002-4355-9838
Shvartzvald, Yossi0000-0003-1525-5041
Yee, Jennifer C.0000-0001-9481-7123
Zang, Weicheng0000-0001-6000-3463
Pogge, Richard W.0000-0003-1435-3053
Mróz, Przemek0000-0001-7016-1692
Skowron, Jan0000-0002-2335-1730
Pietrukowicz, Paweł0000-0002-2339-5899
Ulaczyk, Krzysztof0000-0001-6364-408X
Iwanek, Patryk0000-0002-6212-7221
Bennett, David P.0000-0001-8043-8413
Fukui, Akihiko0000-0002-4909-5763
Itow, Yoshitaka0000-0002-8198-1968
Kondo, Iona0000-0002-3401-1029
Koshimoto, Naoki0000-0003-2302-9562
Miyazaki, Shota0000-0001-9818-1513
Ranc, Clément0000-0003-2388-4534
Rattenbury, Nicholas J.0000-0001-5069-319X
Suzuki, Daisuke0000-0002-5843-9433
Additional Information:© 2020 The American Astronomical Society. Received 2019 October 24; revised 2020 January 22; accepted 2020 January 22; published 2020 February 28. Work by C.H. was supported by the grants of the National Research Foundation of Korea (2017R1A4A1015178 and 2019R1A2C2085965). Work by A.G. was supported by US NSF grant AST-1516842 and by JPL grant 1500811. A.G. received support from the European Research Council under the European Union's Seventh Framework Programme (FP 7) ERC grant Agreement No. [32103]. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. The MOA project is supported by JSPS KAKENHI grant Nos. JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, JP17H02871, and JP16H06287. Y.M. acknowledges the support by the grant JP14002006. D.P.B., A.B., and C.R. were supported by NASA through grant NASA-80NSSC18K0274. The work by C.R. was supported by an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by USRA through a contract with NASA. N.J.R. is a Royal Society of New Zealand Rutherford Discovery Fellow.
Funding AgencyGrant Number
National Research Foundation of Korea2017R1A4A1015178
National Research Foundation of Korea2019R1A2C2085965
European Research Council (ERC)32103
National Science Centre (Poland)MAESTRO 2014/14/A/ST9/00121
Japan Society for the Promotion of Science (JSPS)JSPS24253004
Japan Society for the Promotion of Science (JSPS)JSPS26247023
Japan Society for the Promotion of Science (JSPS)JSPS23340064
Japan Society for the Promotion of Science (JSPS)JSPS15H00781
Japan Society for the Promotion of Science (JSPS)JP17H02871
Japan Society for the Promotion of Science (JSPS)JP16H06287
Japan Society for the Promotion of Science (JSPS)JP14002006
NASA Postdoctoral ProgramUNSPECIFIED
Royal Society of New ZealandUNSPECIFIED
Subject Keywords:Gravitational microlensing; Brown dwarfs
Issue or Number:4
Classification Code:Unified Astronomy Thesaurus concepts: Gravitational microlensing (672); Brown dwarfs (185)
Record Number:CaltechAUTHORS:20200302-135926136
Persistent URL:
Official Citation:Cheongho Han et al 2020 AJ 159 134
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101657
Deposited By: Tony Diaz
Deposited On:02 Mar 2020 22:13
Last Modified:02 Mar 2020 22:13

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