Measuring the Mass of Black Holes with Microlensing

With joint photometric and astrometric microlensing data, we can break degeneracies between lens mass, relative proper motions between the lens and source, and relative distances between the lens and source. We can then measure the mass of the lens, discovering black holes with microlensing.

Simulating a population of microlensing events

We use PopSyCLE, a microlensing population synthesis code, to simulate realisitic populations of microlensing events. These can be used for forecasting, completeness corrections, and heirarchical inference to extract physical parameters such as the black hole mass function and binary fraction.

Ground-based optical & infrared microlensing surveys

Dedicated microlensing surveys monitor the Galactic bulge to discover microlensing events.

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Select BH candidate microlensing from alerts

Microlensing events with long Einstein crossing times and low microlensing parallax are selected for astrometric follow-up.

Einstein timescale and microlensing parallax diagram from PopSyCLE selection criteria

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Observe with Keck AO

High-resolution imaging with Keck adaptive optics (with NIRC2 and OSIRIS) can measure the astrometric shift caused by microlensing.

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Reduce with KAI

The Keck AO Imaging (KAI) data reduction pipeline processes raw Keck images and produces catalogs of photometry and astrometry for each epoch. Note, the pipeline is no longer dependent on IRAF!

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Align astrometry with FlyStar

FlyStar cross-matches reference stars and transforms detector coordinates into a common astrometric frame, tying Keck AO epochs to survey or Gaia reference catalogs.

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Joint photometric–astrometric fit with BAGLE

BAGLE (Bayesian Analysis of Gravitational Lensing Events) performs nested sampling, multi-dataset fits combining survey photometry with high-resolution astrometry to infer microlensing parameters and lens masses.

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Lens masses & classifications

Combined analysis yields physical lens properties, including mass estimates and the likelihood that the lens is a dark remnant (for example a black hole or neutron star) versus a luminous star, informing the Galactic compact-object mass function.

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PopSyCLE

PopSyCLE is a microlensing population synthesis code to generate synthetic microlensing events. It uses Galaxia to generate stellar density and kinematics and SPISEA for compact objects and binary companions.

PopSyCLE Sources

SPISEA Sources

Galaxia Sources

Simulated distributions of microlensing parameters

From PopSyCLE, we can make observability cuts on output events and produce simulated distributions of microlensing parameters.

OGLE tE distribution

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Simulate individual microlensing events with BAGLE

BAGLE can simulate microlensing events including binary lens, binary source, or both with any given time series.

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roman_GBTDS

The Roman Galactic Bulge Time Domain Survey (GBTDS) simulation module produces Roman-like photometric and astrometric time series—encoding the microlensing signal, pixelization, and relative astrometry relevant to Roman’s crowded bulge fields.

Simulate Rubin photometry with LightCurveLynx

With a built-in wrapper around BAGLE, LightCurveLynx simulates microlensing photometry with Rubin cadence and noise.

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Simulate Roman photometry and astromoetry with roman_GBTDS

The Roman Galactic Bulge Time Domain Survey (GBTDS) simulation module produces Roman-like photometric and astrometric time from BAGLE microlensing events. It includes the capability to bin the astrometry.

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