Two new free-floating or wide-orbit planets from microlensing

¹ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland
e-mail: pmroz@astrouw.edu.pl
² Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
³ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
⁴ Korea Astronomy and Space Science Institute, Daejon 34055, Republic of Korea
⁵ Department of Earth and Space Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
⁶ IPAC, Mail Code 100-22, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
⁷ Department of Astronomy, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁸ Department of Physics, University of Warwick, Coventry CV4 7AL, UK
⁹ University of Canterbury, Department of Physics and Astronomy, Private Bag 4800, Christchurch 8020, New Zealand
¹⁰ Korea University of Science and Technology, Daejeon 34113, Republic of Korea
¹¹ Max-Planck-Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹² Department of Physics, Chungbuk National University, Cheongju 28644, Republic of Korea
¹³ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
¹⁴ Physics Department and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
¹⁵ School of Space Research, Kyung Hee University, Yongin, Kyeonggi 17104, Republic of Korea
¹⁶ Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan
¹⁷ Institute of Natural and Mathematical Sciences, Massey University, Auckland 0745, New Zealand
¹⁸ Department of Physics, University of Auckland, Private Bag 92019, Auckland, New Zealand
¹⁹ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁰ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
²¹ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²² National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²³ School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand
²⁴ Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara, Kanagawa, 252-5210, Japan
²⁵ University of Canterbury Mt. John Observatory, PO Box 56, Lake Tekapo 8770, New Zealand
²⁶ Department of Physics, Faculty of Science, Kyoto Sangyo University, 603-8555 Kyoto, Japan
²⁷ School of Physics and Astronomy and Wise Observatory, Tel-Aviv University, Tel-Aviv 6997801, Israel

Received: 1 November 2018
Accepted: 9 January 2019

Abstract

Planet formation theories predict the existence of free-floating planets that have been ejected from their parent systems. Although they emit little or no light, they can be detected during gravitational microlensing events. Microlensing events caused by rogue planets are characterized by very short timescales t_E (typically below two days) and small angular Einstein radii θ_E (up to several μas). Here we present the discovery and characterization of two ultra-short microlensing events identified in data from the Optical Gravitational Lensing Experiment (OGLE) survey, which may have been caused by free-floating or wide-orbit planets. OGLE-2012-BLG-1323 is one of the shortest events discovered thus far (t_E = 0.155 ± 0.005 d, θ_E = 2.37 ± 0.10μas) and was caused by an Earth-mass object in the Galactic disk or a Neptune-mass planet in the Galactic bulge. OGLE-2017-BLG-0560 (t_E = 0.905 ± 0.005 d, θ_E = 38.7 ± 1.6μas) was caused by a Jupiter-mass planet in the Galactic disk or a brown dwarf in the bulge. We rule out stellar companions up to a distance of 6.0 and 3.9 au, respectively. We suggest that the lensing objects, whether located on very wide orbits or free-floating, may originate from the same physical mechanism. Although the sample of ultrashort microlensing events is small, these detections are consistent with low-mass wide-orbit or unbound planets being more common than stars in the Milky Way.