Gravitational microlensing provides a unique opportunity to probe the mass distribution of stars, black holes, and other objects in the Milky Way. Population simulations are necessary to interpret results from microlensing surveys. The contribution from binary objects is often neglected or minimized in analysis of observations and simulations despite the high percentage of binary systems and microlensing's ability to probe binaries. To simulate the population effects, we added multiple systems to Stellar Population Interface for Stellar Evolution and Atmospheres (SPISEA), which simulates stellar clusters. We then inject these multiples into Population Synthesis for Compact-object Lensing Events (PopSyCLE), which simulates Milky Way microlensing surveys. When making OGLE observational selection criteria, we find that 55% of observed microlensing events involve a binary system. Specifically, 14.5% of events have a multiple lens and a single source, 31.7% have a single lens and a multiple source, and 8.8% have a multiple lens and a multiple source. The majority of these events have photometric light curves that appear single and are fit well by a single-lens, single-source model. This suggests that binary source and binary lens−binary source models should be included more frequently in event analysis. The mean Einstein crossing time shifts from 19.1 days for single events only to 21.3 days for single and multiple events, after cutting binary events with multiple peaks. The Einstein crossing time distribution of single and single-peaked multiple events is better aligned with observed distributions from OGLE than singles alone, indicating that multiple systems are a significant missing piece between simulations and reality.
Assessing the Impact of Binary Systems on Microlensing Using SPISEA and PopSyCLE Population Simulations
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Abstract
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© 2025. The Author(s). Published by the American Astronomical Society.
Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Acknowledgement
We thank Guy Nir, Will Dawson, Scott Perkins, and Peter McGill for helpful conversations. This research used resources of the National Energy Research Scientific Computing Center (NERSC), a US Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory, operated under contract No. DE-AC02-05CH11231 using NERSC awards HEP-ERCAP0023758 and HEP-ERCAP0026816. N.S.A., J.R.L., and C.Y.L. acknowledge support from the National Science Foundation under grant No. 1909641 and the Heising-Simons Foundation under grant No. 2022-3542. C.Y.L. acknowledges support from NASA FINESST grant No. 80NSSC21K2043, the H2H8 foundation, a Carnegie Fellowship, and a Harrison Fellowship.
Software References
Numpy (C. R. Harris et al. 2020), Matplotlib (J. D. Hunter 2007), Astropy (Astropy Collaboration et al. 2022), pandas (pandas development team 2022; W. McKinney 2010), SciPy(P. Virtanen et al. 2020), pymultinest (J. Buchner et al. 2014), BAGLE, PopSyCLE (C. Y. Lam et al. 2020), SPISEA (M. W. Hosek et al. 2020).
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Additional details
Related works
- Is new version of
- Discussion Paper: arXiv:2501.03506 (arXiv)
Funding
- United States Department of Energy
- DE-AC02-05CH11231
- National Energy Research Scientific Computing Center
- HEP-ERCAP0023758
- National Energy Research Scientific Computing Center
- HEP-ERCAP0026816
- National Science Foundation
- AST-1909641
- Heising-Simons Foundation
- 2022-3542
- National Aeronautics and Space Administration
- 80NSSC21K2043
- Carnegie Institution for Science
Dates
- Accepted
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2025-01-03Accepted
- Available
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2025-02-06Published