A Neptune-mass Free-floating Planet Candidate Discovered by Microlensing Surveys
Abstract
Current microlensing surveys are sensitive to free-floating planets down to Earth-mass objects. All published microlensing events attributed to unbound planets were identified based on their short timescale (below two days), but lacked an angular Einstein radius measurement (and hence lacked a significant constraint on the lens mass). Here, we present the discovery of a Neptune-mass free-floating planet candidate in the ultrashort (t E = 0.320 ± 0.003 days) microlensing event OGLE-2016-BLG-1540. The event exhibited strong finite-source effects, which allowed us to measure its angular Einstein radius of θ E = 9.2 ± 0.5 μas. There remains, however, a degeneracy between the lens mass and distance. The combination of the source proper motion and source-lens relative proper motion measurements favors a Neptune-mass lens located in the Galactic disk. However, we cannot rule out that the lens is a Saturn-mass object belonging to the bulge population. We exclude stellar companions up to ∼15 au.
- Publication:
-
The Astronomical Journal
- Pub Date:
- March 2018
- DOI:
- 10.3847/1538-3881/aaaae9
- arXiv:
- arXiv:1712.01042
- Bibcode:
- 2018AJ....155..121M
- Keywords:
-
- gravitational lensing: micro;
- planets and satellites: detection;
- Astrophysics - Earth and Planetary Astrophysics
- E-Print:
- accepted to AJ