KMT-2021-BLG-1077L: The fifth confirmed multiplanetary system detected by microlensing

¹ Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
e-mail: cheongho@astroph.chungbuk.ac.kr
² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
³ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁴ Institute of Information and Mathematical Sciences, Massey University, Private Bag 102-904, North Shore Mail Centre, Auckland, New Zealand
⁵ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁶ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
⁷ Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100, Israel
⁸ Center for Astrophysics | Harvard & Smithsonian 60 Garden St., Cambridge, MA 02138, USA
⁹ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁰ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹¹ Korea University of Science and Technology, 217 Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea
¹² Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹³ Laboratory for Exoplanets and Stellar Astrophysics, NASA / Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
¹⁵ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
¹⁶ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁷ Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁸ Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
¹⁹ Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
²⁰ Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut, Mönchhofstr. 12–14, 69120 Heidelberg, Germany
²¹ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
²² Department of Physics, The Catholic University of America, Washington, DC 20064, USA
²³ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa 252-5210, Japan
²⁴ University of Canterbury Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand

Received: 15 March 2022
Accepted: 24 March 2022

Abstract

Aims. The high-magnification microlensing event KMT-2021-BLG-1077 exhibits a subtle and complex anomaly pattern in the region around the peak. We analyze the lensing light curve of the event with the aim of revealing the nature of the anomaly.

Methods. We test various models in combination with several interpretations: that the lens is a binary (2L1S), the source is a binary (1L2S), both the lens and source are binaries (2L2S), or the lens is a triple system (3L1S). We search for the best-fit models under the individual interpretations of the lens and source systems.

Results. We find that the anomaly cannot be explained by the usual three-body (2L1S and 1L2S) models. The 2L2S model improves the fit compared to the three-body models, but it still leaves noticeable residuals. On the other hand, the 3L1S interpretation yields a model explaining all the major anomalous features in the lensing light curve. According to the 3L1S interpretation, the estimated mass ratios of the lens companions to the primary are ~1.56 × 10⁻³ and ~1.75 × 10⁻³, which correspond to ~1.6 and ~1.8 times the Jupiter/Sun mass ratio, respectively, and therefore the lens is a multiplanetary system containing two giant planets. With the constraints of the event time-scale and angular Einstein radius, it is found that the host of the lens system is a low-mass star of mid-to-late M spectral type with amass of M_h = 0.14_−0.07^+0.19 M_Θ, and it hosts two gas giant planets with masses of M_p1 = 0.22_−0.12^+0.31 M_J and M_p2 = 0.25_−0.13^+0.35. The planets lie beyond the snow line of the host with projected separations of a_⊥,p1 = 1.26_−1.08^+1.41 AU and a_⊥,p2 = 0.93_−0.80^+1.05 AU. The planetary system resides in the Galactic bulge at a distance of D_L = 8.24_−1.16^+1.02 kpc. The lens of the event is the fifth confirmed multiplanetary system detected by microlensing following OGLE-2006-BLG-109L, OGLE-2012-BLG-0026L, OGLE-2018-BLG-1011L, and OGLE-2019-BLG-0468L.