KMT-2024-BLG-0404L：由星体、棕色矿星和行星组成的三体微重力系统

We have investigated the lensing event KMT-2024-BLG-0404. The light curve of the event exhibited a complex structure with multiple distinct features, including two prominent caustic spikes, two cusp bumps, and a brief discontinuous feature between the caustic spikes. While a binary-lens model captured the general anomaly pattern, it could not account for a discontinuous anomaly feature between the two caustic spikes. To explore the origin of the unexplained feature, we conducted more advanced modeling beyond the standard binary-lens framework. This investigation demonstrated that the previously unexplained anomaly was resolved by introducing an additional lens component with planetary mass. The estimated masses of the lens components are $M_{\rm p}= 17.3^{+25.5}_{-8.8}~M_{\rm E}$ for the planet, and $M_{\rm h,A}=0.090^{+0.133}_{-0.046}~M_\odot$ and $M_{\rm h,B}=0.026^{+0.038}_{-0.013}~M_\odot$ for the binary host stars. Based on these mass estimates, the lens system is identified as a planetary system where a Uranus-mass planet orbits a binary consisting of a late M dwarf and a brown dwarf. The distance to the planetary system is estimated to be $D_{\rm L} = 7.21^{+0.93}_{-0.97}$~kpc, with an 82\% probability that it resides in the Galactic bulge. This discovery represents the ninth planetary system found through microlensing with a planet orbiting a binary host. Notably, it is the first case where the host consists of both a star and a brown dwarf. 我们调查了微重力事件 KMT-2024-BLG-0404。该事件的光度曲线呈现出复杂结构，包含多个明显特征，包括两个突出的临界尖峰、两个尖端凸起以及两个临界尖峰之间的短暂 discontinuous 特征。虽然二体镜模型捕捉了一般的异常模式，但无法解释两个临界尖峰之间的 discontinuous 异常特征。为探索未解释特征的来源，我们在标准二体镜框架之外进行了更高级的建模。该调查表明，之前无法解释的异常通过引入一个具有行星质量的额外镜面组件得以解决。镜面组件的估计质量为 $M_{\rm p}= 17.3^{+25.5}_{-8.8}~M_{\rm E}$（行星），以及 $M_{\rm h,A}=0.090^{+0.133}_{-0.046}~M_\odot$ 和 $M_{\rm h,B}=0.026^{+0.038}_{-0.013}~M_\odot$（二体宿主星）。基于这些质量估计，镜面系统被识别为一个行星系统，其中一颗 Uranus 质量的行星围绕由晚 M 型红矮星和棕矮星组成的二体系统运行。该行星系统的距离估计为 $D_{\rm L} = 7.21^{+0.93}_{-0.97}$~kpc，有 82\% 的概率位于银河系外缘。该发现代表着通过微重力发现的第九个行星系统，具有行星围绕二体宿主。值得注意的是，这是首次发现宿主系统同时包含星体和棕矮星。