KMT-2019-BLG-1339L: an M Dwarf with a Giant Planet or a Companion Near
  the Planet/Brown Dwarf Boundary
  We analyze KMT-2019-BLG-1339, a microlensing event with an obvious but
incompletely resolved brief anomaly feature around the peak of the light curve.
Although the origin of the anomaly is identified to be a companion to the lens
with a low mass ratio $q$, the interpretation is subject to two different
degeneracy types. The first type is the ambiguity in $\rho$, representing the
angular source radius scaled to the angular radius of the Einstein ring,
$\theta_{\rm E}$, and the other is the $s\leftrightarrow s^{-1}$ degeneracy.
The former type, `finite-source degeneracy', causes ambiguities in both $s$ and
$q$, while the latter induces an ambiguity only in $s$. Here $s$ denotes the
separation (in units of $\theta_{\rm E}$) in projection between the lens
components. We estimate that the lens components have masses $(M_1, M_2)\sim
(0.27^{+0.36}_{-0.15}~M_\odot, 11^{+16}_{-7}~M_{\rm J})$ and $\sim
(0.48^{+0.40}_{-0.28}~M_\odot, 1.3^{+1.1}_{-0.7}~M_{\rm J})$ according to the
two solutions subject to the finite-source degeneracy, indicating that the lens
comprises an M dwarf and a companion with a mass around the planet/brown dwarf
boundary or a Jovian-mass planet. It is possible to lift the finite-source
degeneracy by conducting future observations utilizing a high resolution
instrument because the relative lens-source proper motion predicted by the
solutions are widely different.
