Han CBond IAUdalski ALee C-UGould AAlbrow MDChung S-JHwang K-HJung YKRyu Y-HShvartzvald YShin I-GYee JCYang HZang WCha S-MKim DKim D-JKim S-LLee D-JLee YPark B-GPogge RWAbe FBando KBarry RBennett DPBhattacharya AFujii HFukui AHamada RHamada SHamasaki NHirao YIshitani Silva SItow YKirikawa RKoshimoto NMatsubara YMiyazaki SMuraki YNagai TNunota KOlmschenk GRanc CRattenbury NJSatoh YSumi TSuzuki DTomoyoshi MTristram PJVandorou AYama HYamashita KMróz PSzymański MKSkowron JPoleski RASoszyński IPietrukowicz PKozłowski SRybicki KAIwanek PUlaczyk KWrona MGromadzki MMróz MJ2025-01-142025-01-142024-07Han C, Bond IA, Udalski A, Lee CU, Gould A, Albrow MD, Chung SJ, Hwang KH, Jung YK, Ryu YH, Shvartzvald Y, Shin IG, Yee JC, Yang H, Zang W, Cha SM, Kim D, Kim DJ, Kim SL, Lee DJ, Lee Y, Park BG, Pogge RW, Abe F, Bando K, Barry R, Bennett DP, Bhattacharya A, Fujii H, Fukui A, Hamada R, Hamada S, Hamasaki N, Hirao Y, Ishitani Silva S, Itow Y, Kirikawa R, Koshimoto N, Matsubara Y, Miyazaki S, Muraki Y, Nagai T, Nunota K, Olmschenk G, Ranc C, Rattenbury NJ, Satoh Y, Sumi T, Suzuki D, Tomoyoshi M, Tristram PJ, Vandorou A, Yama H, Yamashita K, Mróz P, Szymański MK, Skowron J, Poleski RA, Soszyński I, Pietrukowicz P, Kozłowski S, Rybicki KA, Iwanek P, Ulaczyk K, Wrona M, Gromadzki M, Mróz MJ. (2024). KMT-2023-BLG-1866Lb: Microlensing super-Earth around an M dwarf host. Astronomy and Astrophysics. 687. July 2021.0004-6361https://mro.massey.ac.nz/handle/10179/72371Aims. We aim to investigate the nature of the short-term anomaly that appears in the lensing light curve of KMT-2023-BLG-1866. The anomaly was only partly covered due to its short duration of less than a day, coupled with cloudy weather conditions and a restricted nighttime duration. Methods. Considering the intricacy of interpreting partially covered signals, we thoroughly explored all potential degenerate solutions. Through this process, we identified three planetary scenarios that account for the observed anomaly equally well. These scenarios are characterized by the specific planetary parameters: (s, q)inner = [0.9740 ± 0.0083, (2.46 ± 1.07) × 10-5], (s, q)intermediate = [0.9779 ± 0.0017, (1.56 ± 0.25) × 10-5], and (s, q)outer = [0.9894 ± 0.0107, (2.31 ± 1.29) × 10-5], where s and q denote the projected separation (scaled to the Einstein radius) and mass ratio between the planet and its host, respectively. We identify that the ambiguity between the inner and outer solutions stems from the inner-outer degeneracy, while the similarity between the intermediate solution and the others is due to an accidental degeneracy caused by incomplete anomaly coverage. Results. Through Bayesian analysis utilizing the constraints derived from measured lensing observables and blending flux, our estimation indicates that the lens system comprises a very-low-mass planet orbiting an early M-type star situated approximately (6.2-6.5) kpc from Earth in terms of median posterior values for the different solutions. The median mass of the planet host is in the range of (0.48-0.51) M⊙, and that of the planet's mass spans a range of (2.6-4.0) ME, varying across different solutions. The detection of KMT-2023-BLG-1866Lb signifies the extension of the lensing surveys to very-low-mass planets that have been difficult to detect in earlier surveys.(c) The author/shttps://creativecommons.org/licenses/by/4.0/gravitational lensingmicro / planets and satellitesdetectionJournal article10.1051/0004-6361/2024496181432-0746CC BYjournal-articleA241