标题： 朝麦哲伦云的一次二元透镜事件：观测与暗物质启示 显示英文标题

标题： A Binary Lensing Event Toward the LMC: Observations and Dark Matter Implications

摘要： MACHO合作组织最近分析了大约850万颗位于大麦哲伦云（LMC）的恒星在2.1年的测光数据。这一分析揭示了8个候选微引力透镜事件和总微引力透镜光学深度为$\tau_{meas} = 2.9 +1.4/-0.9 \times 10^{-7}$。这远远超过了从已知恒星群体预测的事件数量（1.1）和微引力透镜光学深度：$\tau_{back} = 5.4\times 10^{-8}$，但与大约一半的标准暗晕质量由质量为$\sim 0.5 \msun$的Machos组成的模型一致。 在这8个事件中，有一个似乎是一个双透镜事件，其焦散线交叉部分被部分解析，从而允许我们估算透镜的距离。如果源恒星不是一个短周期双星系统，那么透镜系统很可能位于LMC中。然而，如果我们假设LMC-LMC透镜的光学深度足以解释我们的整个透镜信号，那么这个双星事件似乎并不符合由LMC中的双星对单个LMC源恒星的透镜效应。因此，尽管双透镜可能确实位于LMC中，但没有迹象表明大多数透镜位于LMC中。 显示英文摘要

摘要： The MACHO collaboration has recently analyzed 2.1 years of photometric data for about 8.5 million stars in the Large Magellanic Cloud (LMC). This analysis has revealed 8 candidate microlensing events and a total microlensing optical depth of $\tau_{meas} = 2.9 +1.4/-0.9 \times 10^{-7}$. This significantly exceeds the number of events (1.1) and the microlensing optical depth predicted from known stellar populations: $\tau_{back} = 5.4\times 10^{-8}$, but it is consistent with models in which about half of the standard dark halo mass is composed of Machos of mass $\sim 0.5 \msun$. One of these 8 events appears to be a binary lensing event with a caustic crossing that is partially resolved which allows us to estimate the distance to the lenses. If the source star is not a short period binary star, then we show that the lens system is very likely to reside in the LMC. However, if we assume that the optical depth for LMC-LMC lensing is large enough to account for our entire lensing signal, then the binary event does not appear to be consistent with lensing of a single LMC source star by a binary residing in the LMC. Thus, while the binary lens may indeed reside in the LMC, there is no indication that most of the lenses reside in the LMC.