OGLE-2019-BLG-0960Lb: The Smallest Microlensing Planet
Creators: name: Yee, Jennifer C.
name: Zang, Weicheng
name: Udalski, Andrzej
name: Ryu, Yoon-Hyun
name: Green, Jonathan
name: Hennerley, Steve
name: Marmont, Andrew
name: Sumi, Takahiro
name: Mao, Shude
name: Gromadzki, Mariusz
name: Mróz, Przemek
name: Skowron, Jan
name: Poleski, Radoslaw
name: Szymański, Michał K.
name: Soszyński, Igor
name: Pietrukowicz, Paweł
name: Kozłowski, Szymon
name: Ulaczyk, Krzysztof
name: Rybicki, Krzysztof A.
name: Iwanek, Patryk
name: Wrona, Marcin
name: Albrow, Michael D.
name: Chung, Sun-Ju
name: Gould, Andrew
name: Han, Cheongho
name: Hwang, Kyu-Ha
name: Jung, Youn Kil
name: Kim, Hyoun-Woo
name: Shin, In-Gu
name: Shvartzvald, Yossi
name: Cha, Sang-Mok
name: Kim, Dong-Jin
name: Kim, Seung-Lee
name: Lee, Chung-Uk
name: Lee, Dong-Joo
name: Lee, Yongseok
name: Park, Byeong-Gon
name: Pogge, Richard W.
name: Bachelet, Etienne
name: Christie, Grant
name: Hundertmark, Markus P. G.
name: Maoz, Dan
name: McCormick, Jennie
name: Natusch, Tim
name: Penny, Matthew T.
name: Street, Rachel A.
name: Tsapras, Yiannis
name: Beichman, Charles A.
name: Bryden, Geoffery
name: Novati, Sebastiano Calchi
name: Carey, Sean
name: Gaudi, B. Scott
name: Henderson, Calen B.
name: Johnson, Samson
name: Zhu, Wei
name: Bond, Ian A.
name: Abe, Fumio
name: Barry, Richard
name: Bennett, David P.
name: Bhattacharya, Aparna
name: Donachie, Martin
name: Fujii, Hirosane
name: Fukui, Akihiko
name: Hirao, Yuki
name: Silva, Stela Ishitani
name: Itow, Yoshitaka
name: Kirikawa, Rintaro
name: Kondo, Iona
name: Koshimoto, Naoki
name: Li, Man Cheung Alex
name: Matsubara, Yutaka
name: Muraki, Yasushi
name: Miyazaki, Shota
name: Olmschenk, Greg
name: Ranc, Clément
name: Rattenbury, Nicholas J.
name: Satoh, Yuki
name: Shoji, Hikaru
name: Suzuki, Daisuke
name: Tanaka, Yuzuru
name: Tristram, Paul J.
name: Yamawaki, Tsubasa
name: Yonehara, Atsunori
Publisher: name: arXiv
Year: 2021
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the analysis of OGLE-2019-BLG-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2--1.6 x 10^{-5} at 1-sigma). Although there is substantial uncertainty in the satellite parallax measured by Spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (M_L = 0.3--0.6 M_Sun), the mass of its planet (m_p = 1.4--3.1 M_Earth), the projected separation between the host and planet (a_perp = 1.2--2.3 au), and the distance to the lens system (D_L = 0.6--1.2 kpc). The lens is plausibly the blend, which could be checked with adaptive optics observations. As the smallest planet clearly below the break in the mass-ratio function (Suzuki et al. 2016; Jung et al. 2019), it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. We find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor A &gt; 5. Finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s &gt; 1) and (s &lt; 1) solutions are not in the regime (|log s| &gt;&gt; 0) for which the "close"/"wide" degeneracy was derived. This investigation suggests a link between the "close"/"wide" and "inner/outer" degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases.
description: 32 pages, 15 figures, 5 tables. Submitted to AAS Journals