Analyses of anomalous lensing events detected from the UKIRT microlensing survey

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
² Center for Astrophysics | Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
³ Department of Astronomy, Tsinghua University, Beijing 100084, China
⁴ Astronomical Observatory, University of Warsaw, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
⁵ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁶ Institute of Natural and Mathematical Science, Massey University, Auckland 0745, New Zealand
⁷ School of Physics and Astronomy, Sun Yat-sen University, Zhuhai 519082, PR China
⁸ CSST Science Center for the Guangdong-Hong Kong-Macau Great Bay Area, Sun Yat-sen University, Zhuhai 519082, China
⁹ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
¹⁰ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
¹¹ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹² Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
¹³ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
¹⁴ Villanova University, Department of Astrophysics and Planetary Sciences, 800 Lancaster Ave., Villanova, PA 19085, USA
¹⁵ Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹⁶ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁷ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁸ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁹ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²⁰ Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
²¹ Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
²² Oak Ridge Associated Universities, Oak Ridge, TN 37830, USA
²³ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
²⁴ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
²⁵ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
²⁶ University of Canterbury Mt. John Observatory, P.O. Box 56, Lake Tekapo 8770, New Zealand

^★ Corresponding author; leecu@kasi.re.kr

Received: 20 January 2025
Accepted: 18 March 2025

Abstract

Aims. The United Kingdom Infrared Telescope (UKIRT) microlensing survey was conducted over four years, from 2016 to 2019, with the goal of serving as a precursor to future near-infrared microlensing surveys. Focusing on stars in the Galactic center and utilizing near-infrared passbands, the survey identified approximately one thousand microlensing events, 27 of which displayed anomalies in their light curves. This paper presents an analysis of these anomalous events, aiming to uncover the underlying causes of the observed anomalies.

Methods. The events were analyzed under various configurations, considering the potential binarity of both the lens and the source. For 11 events that were additionally observed by other optical microlensing surveys, including those conducted by the OGLE, KMTNet, and MOA collaborations, we incorporated their data into our analysis.

Results. Among the reported anomalous events, we revealed the nature of 24 events except for three events, in which one was likely to be a transient variable, and two were difficult to accurately characterize their nature due to the limitations of the available data. We confirmed the binary lens nature of the anomalies in 22 events. Among these, we verified the earlier discovery that the companion in the binary lens system UKIRT11L is a planetary object. Accurately describing the anomaly in UKIRT21 required a model that accounted for the binarity of both the lens and the source. For two events UKIRT01 and UKIRT17, the anomalies could be interpreted using either a binary-source or a binary-lens model. For the UKIRT05, it was found that accounting for higher-order effects induced by the orbit al motions of both Earth and the binary lens was crucial. With the measured microlensing parallax togeter with the angular Einstein radius, the component masses of the UKIRT05 binary lens were determined to be M₁ = (1.05 ± 0.20) M_⊙, M₂ = (0.36 ± 0.07) M_⊙, and the distance to the lens was found to be D_L = (3.11 ± 0.40) kpc.