We report the discovery of the planet OGLE-2018-BLG-0532Lb, with very obvious signatures in the light curve that lead to an estimate of the planet-host mass ratio $q=M_{\rm planet}/M_{\rm host}\simeq 1\times10^{-4}$. Although there are no obvious systematic residuals to this double-lens/single-source (2L1S) fit, we find that $\chi^2$ can be significantly improved by adding either a third lens (3L1S, $\Delta\chi^2=81$) or second source (2L2S, $\Delta\chi^2=65$) to the lens-source geometry. After thorough investigation, we conclude that we cannot decisively distinguish between these two scenarios and therefore focus on the robustly-detected planet. However, given the possible presence of a second planet, we investigate to what degree and with what probability such additional planets may affect seemingly single-planet light curves. Our best estimates for the properties of the lens star and the secure planet are: a host mass $M\sim 0.25\,M_\odot$, system distance $D_L\sim 1\,$kpc and planet mass $m_{p,1}= 8\,M_\oplus$ with projected separation $a_{1,\perp}=1.4\,$au. However, there is a relatively bright $I=18.6$ (and also relatively blue) star projected within $<50\,$mas of the lens, and if future high-resolution images show that this is coincident with the lens, then it is possible that it is the lens, in which case, the lens would be both more massive and more distant than the best-estimated values above.

中文翻译：

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OGLE-2018-BLG-0532Lb：冷海王星与可能的木星兄弟姐妹

我们报告了 OGLE-2018-BLG-0532Lb 行星的发现，在光变曲线中有非常明显的特征，导致估计行星与宿主的质量比 $q=M_{\rm Planet}/M_{\rm host }\simeq 1\times10^{-4}$。虽然这种双镜头/单源 (2L1S) 拟合没有明显的系统残差，但我们发现 $\chi^2$ 可以通过添加第三个镜头 (3L1S, $\Delta\chi^2 =81$) 或第二个源 (2L2S, $\Delta\chi^2=65$) 到透镜源几何结构。经过彻底调查，我们得出结论，我们无法决定性地区分这两种情况，因此将重点放在被可靠检测到的行星上。然而，考虑到可能存在第二颗行星，我们调查了这些额外的行星在何种程度上以及以何种概率影响看似单行星的光变曲线。我们对透镜星和安全行星属性的最佳估计是：宿主质量 $M\sim 0.25\,M_\odot$，系统距离 $D_L\sim 1\,$kpc 和行星质量 $m_{p, 1}= 8\,M_\oplus$ 投影分离 $a_{1,\perp}=1.4\,$au。然而，在镜头的 $<50\,$mas 内投射了一颗比较亮的 $I=18.6$（也比较蓝）的星星，如果未来的高分辨率图像显示这与镜头重合，那么它可能是镜头，在这种情况下，镜头的质量会比上面的最佳估计值更大，也更远。