We report the discovery and the analysis of the short (tE < 5 days) planetary microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical Gravitational Lensing Experiment (OGLE), and the planetary anomaly (at I ~ 19) was captured by The Korea Microlensing Telescope Network (KMTNet). The event has three surviving planetary models that explain the observed light curves, with planet-host mass ratio q \~ 5.4 * 10^{-3}, 4.5 * 10^{-3} and 4.5 * 10^{-2}, respectively. The first model is the best-fit model, while the second model is disfavored by \Delta\chi^2 ~ 3. The last model is strongly disfavored by \Delta\chi^2 ~ 15 but not ruled out. A Bayesian analysis using a Galactic model indicates that the first two models are probably composed of a Saturn-mass planet orbiting a late M dwarf, while the third one could consist of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative proper motion is mu_rel ~ 9 mas/yr, so the source and lens could be resolved by current adaptive-optics (AO) instruments in 2021 if the lens is luminous.
@article{arxiv.1911.02439,
title = {OGLE-2015-BLG-1771Lb: A Microlens Planet Orbiting an Ultracool Dwarf?},
author = {Xiangyu Zhang and Weicheng Zang and Andrzej Udalski and Andrew Gould and Yoon-Hyun Ryu and Tianshu Wang and Hongjing Yang and Shude Mao and Przemek Mróz and Jan Skowron and Radoslaw Poleski and Michał K. Szymański and Igor Soszyński and Paweł Pietrukowicz and Szymon Kozłowski and Krzysztof Ulaczyk and Michael D. Albrow and Sun-Ju Chung and Cheongho Han and Kyu-Ha Hwang and Youn Kil Jung and In-Gu Shin and Yossi Shvartzvald and Jennifer C. Yee and Wei Zhu and Sang-Mok Cha and Dong-Jin Kim and Hyoun-Woo Kim and Seung-Lee Kim and Chung-Uk Lee and Dong-Joo Lee and Yongseok Lee and Byeong-Gon Park and Richard W. Pogge},
journal= {arXiv preprint arXiv:1911.02439},
year = {2020}
}