OGLE-2013-BLG-0911Lb: A Secondary on the Brown-Dwarf Planet Boundary
  around an M-dwarf
  We present the analysis of the binary-lens microlensing event
OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of
q~0.03 which differs from that reported in Shvartzvald+2016. The event suffers
from the well-known close/wide degeneracy, resulting in two groups of solutions
for the projected separation normalized by the Einstein radius of s~0.15 or
s~7. The finite source and the parallax observations allow us to measure the
lens physical parameters. The lens system is an M-dwarf orbited by a massive
Jupiter companion at very close (M_{host}=0.30^{+0.08}_{-0.06} M_{Sun},
M_{comp}=10.1^{+2.9}_{-2.2} M_{Jup}, a_{exp}=0.40^{+0.05}_{-0.04} au) or wide
(M_{host}=0.28^{+0.10}_{-0.08} M_{Sun}, M_{comp}=9.9^{+3.8}_{-3.5}M_{Jup},
a_{exp}=18.0^{+3.2}_{-3.2} au) separation. Although the mass ratio is slightly
above the planet-brown dwarf (BD) mass-ratio boundary of q=0.03 which is
generally used, the median physical mass of the companion is slightly below the
planet-BD mass boundary of 13M_{Jup}. It is likely that the formation
mechanisms for BDs and planets are different and the objects near the
boundaries could have been formed by either mechanism. It is important to probe
the distribution of such companions with masses of ~13M_{Jup} in order to
statistically constrain the formation theories for both BDs and massive
planets. In particular, the microlensing method is able to probe the
distribution around low-mass M-dwarfs and even BDs which is challenging for
other exoplanet detection methods.
