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(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(E) less than or similar to 6 days) but also with very small angular Einstein radii (theta(E) less than or similar to 0.05 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 Monte Carlo simulations of Galactic events conducted with the combined t(E) and theta(E) constraint, it is estimated that the lens masses of the individual events are 0.051(-0.027)(-0.100) M-circle dot, 0.044(-0.023)(+0.090)M(circle dot), and 0.046(-0.023)(+0.067) M-circle dot/0.038(-0.019)(+0.056) M-circle dot and the probability of the lens mass smaller than the lower limit of stars is similar to 80% for all events. We point out that routine lens mass measurements of short-timescale lensing events require survey-mode space-based observations.

Candidate Brown-dwarf Microlensing Events with Very Short Timescales and Small Angular Einstein Radii

Bozza, V
Validation
;
2020

Abstract

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(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(E) less than or similar to 6 days) but also with very small angular Einstein radii (theta(E) less than or similar to 0.05 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 Monte Carlo simulations of Galactic events conducted with the combined t(E) and theta(E) constraint, it is estimated that the lens masses of the individual events are 0.051(-0.027)(-0.100) M-circle dot, 0.044(-0.023)(+0.090)M(circle dot), and 0.046(-0.023)(+0.067) M-circle dot/0.038(-0.019)(+0.056) M-circle dot and the probability of the lens mass smaller than the lower limit of stars is similar to 80% for all events. We point out that routine lens mass measurements of short-timescale lensing events require survey-mode space-based observations.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11386/4737759
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