KMT-2019-BLG-1339L: an M Dwarf with a Giant Planet or a Companion Near the Planet/Brown Dwarf Boundary

Abstract

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 $\ddot{I}$, representing the angular source radius scaled to the angular radius of the Einstein ring, $\hat{I}{¸}_{\mathrm{E}}$, 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 $\hat{I}{¸}_{\mathrm{E}}$) in projection between the lens components. We estimate that the lens components have masses $(M_1,M_2)\sim (0.27_{-0.15}^{+0.36}{M}_{\odot },11_{-7}^{+16}{M}_{\mathrm{J}})$ and $\sim (0.48_{-0.28}^{+0.40}{M}_{\odot },1.3_{-0.7}^{+1.1}{M}_{\mathrm{J}})$ 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.

8 pages, 6 figures