Two Low-Mass-Ratio Microlensing Planets from High-Magnification Events: KMT-2021-BLG-0247 and MOA-2023-BLG-169

Abstract

We present an analysis of two planetary microlensing events, KMT-2021-BLG-0247 and MOA-2023-BLG-169, both of which exhibit high magnifications and low planet--host mass ratios, but with markedly different levels of parameter constraint. For KMT-2021-BLG-0247, the finite-source effect and microlens parallax are both clearly detected, leading to unusually tight constraints on the physical properties of the lens system. The host mass and lens distance are approximately $M_{\mathrm{L}}=0.9\pm 0.1M_{\odot }$ and $D_{\mathrm{L}}=6.7_{-0.3}^{+1.0}\mathrm{kpc}$, respectively, and the planet mass is $M_{\mathrm{p}}=41\pm 5M_{\oplus }$. The projected planet--host separations are $a_{\perp }=3.4_{-0.3}^{+0.7}\mathrm{au}$ and $3.0_{-0.3}^{+0.6}\mathrm{au}$ for the wide and close solutions, respectively. In contrast, MOA-2023-BLG-169 involves an extremely faint source, with $I_{S,\mathrm{OGLE}}=26.73$, such that the light curve permits a broad family of strongly correlated solutions. We therefore construct the physical-parameter likelihood using approximate invariant combinations of the light-curve parameters and supplement it with post-event Euclid/VIS imaging from the Euclid Q2 Galactic Bulge Survey (Beaulieu et al. 2026). The Euclid data reveal a component at the event position with ${\mathrm{VIS}}_{\mathrm{AB}}=23.05\pm 0.09\mathrm{mag}$. Interpreting this component as the combined light from the source and any luminous lens, the resulting posterior gives $M_{\mathrm{L}}=0.48_{-0.17}^{+0.23}{M}_{\odot }$, $D_{\mathrm{L}}=3.50_{-1.20}^{+2.82}\mathrm{kpc}$, $a_{\perp }=1.62_{-0.43}^{+0.77}\mathrm{au}$, and $M_{\mathrm{p}}=143_{-63}^{+103}{M}_{\oplus }$. MOA-2023-BLG-169 demonstrates that, for an extreme faint-source event, even the event timescale and angular Einstein radius can remain strongly dependent on the Galactic prior and independent flux constraints.

The manuscript was inadvertently submitted before all relevant collaborators had an opportunity to review it, and the author list is incomplete. A revised version will be posted after completing the coauthor review