极端有限源效应下微透镜事件的多参数简并
A Multi-Parameter Degeneracy in Microlensing Events with Extreme Finite Source Effects
摘要：
对于质量足够低的微透镜，源星的角半径可以远大于透镜的爱因斯坦环角半径。对于这样的极端有限源效应（EFSE）事件，有限源效应占主导地位的整个事件的持续时间。在这里，我们证明和探索的EFSE事件的多个参数之间的连续简并。简并度中的第一个分量来自于这样一个事实，即直接可观察到的通量峰值变化取决于源角半径与爱因斯坦环角半径的比值以及可归因于透镜源星的基线通量的分数。第二个分量的出现是因为事件的直接可观察的持续时间取决于事件的碰撞参量和相对透镜源自行。这两个成对的简并成为耦合时，光变曲线的详细形态被认为是，特别是当包括一个边缘变暗的配置文件的源星。我们推导出这些退化数学通过解析近似，并进一步研究它们的数值没有近似。我们探讨了这些数学退化可能实现和可能被打破的可能物理情况。随着越来越多的低质量透镜事件（随着爱因斯坦环半径的不断减小）被检测到，微透镜调查的精度和节奏越来越高，人们可以预期将发现更多的EFSE事件。特别是，EFSE微透镜事件的检测可能会随着罗马太空望远镜银河系膨胀时域巡天而急剧增加。
英文摘要：
For microlenses with sufficiently low mass, the angular radius of the source star can be much larger than the angular Einstein ring radius of the lens. For such extreme finite source effect (EFSE) events, finite source effects dominate throughout the duration of the event. Here, we demonstrate and explore a continuous degeneracy between multiple parameters of such EFSE events. The first component in the degeneracy arises from the fact that the directly-observable peak change of the flux depends on both the ratio of the angular source radius to the angular Einstein ring radius and the fraction of the baseline flux that is attributable to the lensed source star. The second component arises because the directly-observable duration of the event depends on both the impact parameter of the event and the relative lens-source proper motion. These two pairwise degeneracies become coupled when the detailed morphology of the light curve is considered, especially when including a limb-darkening profile of the source star. We derive these degeneracies mathematically through analytic approximations and investigate them further numerically with no approximations. We explore the likely physical situations in which these mathematical degeneracies may be realized and potentially broken. As more and more low-mass lensing events (with ever decreasing Einstein ring radii) are detected with improving precision and increasing cadence from microlensing surveys, one can expect that more of these EFSE events will be discovered. In particular, the detection of EFSE microlensing events could increase dramatically with the Roman Space Telescope Galactic Bulge Time Domain Survey.
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