KMT-2021-BLG-1547Lb: Giant microlensing planet detected through a signal deformed due to source binarity

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Center for Astrophysics | Harvard & Smithsonian, 60 Garden St., Cambridge, MA 02138, USA
³ Department of Astronomy, Tsinghua University, Beijing 100084, PR China
⁴ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁵ Korea University of Science and Technology, Korea, (UST), 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
⁶ Institute of Natural and Mathematical Science, Massey University, Auckland 0745, New Zealand
⁷ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁸ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
¹⁰ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
¹¹ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹² Klein Karoo Observatory, Calitzdorp, and Bronberg Observatory, Pretoria, South Africa
¹³ Kavli Institute for Astronomy and Astrophysics, Peking University, Yi He Yuan Road 5, Hai Dian District, Beijing 100871, PR China
¹⁴ School of Physics and Astronomy, Tel-Aviv University, Tel-Aviv 6997801, Israel
¹⁵ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803, USA
¹⁶ Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹⁷ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁸ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁹ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁰ Instituto de Astrofisica de Canarias, Via Lâctea s/n, 38205 La Laguna, Tenerife, Spain
²¹ Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
²² Institute of Astronomy, Graduate School of Science, The University of Tokyo, 2-21-1 Osawa, Mitaka, Tokyo 181-0015, Japan
²³ Department of Physics, The Catholic University of America, Washington, DC 20064, USA
²⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁵ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
²⁶ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
²⁷ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
²⁸ University of Canterbury Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand

Received: 5 July 2023
Accepted: 31 August 2023

Abstract

Aims. We investigate the previous microlensing data collected by the KMTNet survey in search of anomalous events for which no precise interpretations of the anomalies had been suggested. From this investigation, we find that the anomaly in the lensing light curve of the event KMT-2021-BLG-1547 is approximately described by a binary-lens (2L1S) model with a lens possessing a giant planet, but the model leaves unexplained residuals.

Methods. We investigated the origin of the residuals by testing more sophisticated models that include either an extra lens component (3L1S model) or an extra source star (2L2S model) on top of the 2L1S configuration of the lens system. From these analyses, we find that the residuals from the 2L1S model originate from the existence of a faint companion to the source. The 2L2S solution substantially reduces the residuals and improves the model fit by Δχ² = 67.1 with respect to the 2L1S solution. The 3L1S solution also improves the fit, but its fit is worse than that of the 2L2S solution by Δχ² = 24.7.

Results. According to the 2L2S solution, the lens of the event is a planetary system with planet and host masses (M_p/M_J, M_h/M_⊙) = (1.47_−0.77^+0.64, 0.72_−0.38^+0.32) lying at a distance D_L = 5.07_−1.50^+0.98 kpc, and the source is a binary composed of a subgiant primary of a late G or an early K spectral type and a main-sequence companion of a K spectral type. The event demonstrates the need for sophisticated modeling of unexplained anomalies if one wants to construct a complete microlensing planet sample.