KMT-2017-BLG-2820 and the Nature of the Free-floating Planet Population
Yoon-Hyun Ryu, Przemek Mróz, Andrew Gould, Kyu-Ha Hwang, Hyoun-Woo Kim, Jennifer C. Yee, and, Michael D. Albrow, Sun-Ju Chung, Youn Kil Jung, In-Gu Shin, Yossi Shvartzvald, Weicheng Zang, Sang-Mok Cha, Dong-Jin Kim, Seung-Lee Kim, Chung-Uk Lee, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Cheongho Han, Richard W. Pogge, Andrzej Udalski, Radek Poleski, Jan Skowron, Michał K. Szymański, Igor Soszyński, Paweł Pietrukowicz, Szymon Kozłowski, Krzysztof Ulaczyk, Krzysztof A. Rybicki, Patryk Iwanek
Abstract
Abstract We report a new free-floating planet (FFP) candidate, KMT-2017-BLG-2820, with Einstein radius θ E ≃ 6 μ as, lens-source relative proper motion μ rel ≃ 8 mas yr −1 , and Einstein timescale t E = 6.5 hr. It is the third FFP candidate found in an ongoing study of giant-source finite-source point-lens (FSPL) events in the KMTNet database and the sixth FSPL FFP candidate overall. We find no significant evidence for a host. Based on their timescale distributions and detection rates, we argue that five of these six FSPL FFP candidates are drawn from the same population as the six point-source point-lens (PSPL) FFP candidates found by Mróz et al. in the OGLE-IV database. The θ E distribution of the FSPL FFPs implies that they are either sub-Jovian planets in the bulge or super-Earths in the disk. However, the apparent “Einstein desert” (10 ≲ θ E / μ as ≲ 30) would argue for the latter. Whether each of the 12 (six FSPL and six PSPL) FFP candidates is truly an FFP or simply a very wide-separation planet can be determined at first adaptive optics (AO) light on 30 m telescopes, and earlier for some. If the latter, a second epoch of AO observations could measure the projected planet–host separation with a precision of . At the present time, the balance of evidence favors the unbound-planet hypothesis.