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تسجيل مستخدم جديدCandidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii
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Short-timescale microlensing events are likely to be produced by substellar brown dwarfs (BDs), but it is difficult to securely identify BD lenses based on only event timescales $t_{rm E}$ because short-timescale events can also be produced by stellar lenses with high relative lens-source proper motions. In this paper, we report three strong candidate BD-lens events found from the search for lensing events not only with short timescales ($t_{rm E} lesssim 6~{rm days}$) but also with very small angular Einstein radii ($theta_{rm E}lesssim 0.05~{rm mas}$) among the events that have been found in the 2016--2019 observing seasons. These events include MOA-2017-BLG-147, MOA-2017-BLG-241, and MOA-2019-BLG-256, in which the first two events are produced by single lenses and the last event is produced by a binary lens. From the Bayesian analysis conducted with the combined $t_{rm E}$ and $theta_{rm E}$ constraint, it is estimated that the lens masses of the individual events are $0.051^{+0.100}_{-0.027}~M_odot$, $0.044^{+0.090}_{-0.023}~M_odot$, and $0.046^{+0.067}_{-0.023}~M_odot/0.038^{+0.056}_{-0.019}~M_odot$ and the probability of the lens mass smaller than the lower limit of stars is $sim 80%$ for all events. We point out that routine lens mass measurements of short time-scale lensing events require survey-mode space-based observations.
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