OGLE-2015-BLG-1771Lb: A Microlens Planet Orbiting an Ultracool Dwarf?
  We report the discovery and the analysis of the short (tE < 5 days) planetary
microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical
Gravitational Lensing Experiment (OGLE), and the planetary anomaly (at I ~ 19)
was captured by The Korea Microlensing Telescope Network (KMTNet). The event
has three surviving planetary models that explain the observed light curves,
with planet-host mass ratio q \~ 5.4 * 10^{-3}, 4.5 * 10^{-3} and 4.5 *
10^{-2}, respectively. The first model is the best-fit model, while the second
model is disfavored by \Delta\chi^2 ~ 3. The last model is strongly disfavored
by \Delta\chi^2 ~ 15 but not ruled out. A Bayesian analysis using a Galactic
model indicates that the first two models are probably composed of a
Saturn-mass planet orbiting a late M dwarf, while the third one could consist
of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative
proper motion is mu_rel ~ 9 mas/yr, so the source and lens could be resolved by
current adaptive-optics (AO) instruments in 2021 if the lens is luminous.
