KMT-2019-BLG-2073: Fourth Free-floating Planet Candidate with θ <sub>E</sub> < 10 μas
Hyoun-Woo Kim, Kyu-Ha Hwang, Andrew Gould, Jennifer C. Yee, Yoon-Hyun Ryu, Michael D. Albrow, Sun-Ju Chung, Cheongho Han, Youn Kil Jung, Chung-Uk Lee, In-Gu Shin, Yossi Shvartzvald, Weicheng Zang, Sang-Mok Cha, Dong-Jin Kim, Seung-Lee Kim, Dong-Joo Lee, Yongseok Lee, Byeong-Gon Park, Richard W. Pogge
Abstract
Abstract We analyze the very short Einstein timescale ( t E ≃ 7 hr) event KMT-2019-BLG-2073. Making use of the pronounced finite-source effects generated by the clump giant source, we measure the Einstein radius θ E ≃ 4.8 μ as and so infer a mass <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>M</mml:mi> <mml:mo>=</mml:mo> <mml:mn>59</mml:mn> <mml:mspace width="0.25em"/> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊕</mml:mo> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>π</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>rel</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>16</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>μ</mml:mi> <mml:mi>as</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> , where π rel is the lens-source relative parallax. We find no significant evidence for a host of this planetary-mass object, though one could be present at sufficiently wide separation. If so, it would be detectable after about 10 yr. This is the fourth isolated microlens with a measured Einstein radius θ E < 10 μ as, which we argue is a useful threshold for a “likely free-floating planet (FFP)” candidate. We outline a new approach to constructing a homogeneous sample of giant-star finite-source/point-lens (FSPL) events, within which the subsample of FFP candidates can be statistically analyzed. We illustrate this approach using 2019 KMTNet data and show that there appears to be a large θ E gap between the two FFP candidates and the 11 other FSPL events. We argue that such sharp features are more identifiable in a sample selected on θ E compared to the traditional approach of identifying candidates based on short t E .