  In the near future, wide field surveys will discover 1000's of new strongly
lensed quasars, and these will be monitored with unprecedented cadence by the
Legacy Survey of Space and Time (LSST). Many of these will undergo
caustic-crossing microlensing events over the 10-year LSST survey, in which a
sharp caustic feature from a stellar body in the lensing galaxy crosses the
inner accretion disk. Caustic-crossing events offer the unique opportunity to
probe the vicinity of the central supermassive black hole for 100s of quasars
with multi-platform follow-up triggered by LSST monitoring. To prepare for
these observations, we have developed detailed simulations of caustic-crossing
light curves. These employ a realistic analytic model of the inner accretion
disk that reveals the strong surface brightness asymmetries introduced when
fully accounting for both special- and general-relativistic effects. We
demonstrate that an inflection in the caustic-crossing light curve due to the
innermost stable circular orbit (ISCO) can be detected in reasonable follow-up
observations and can be analyzed to constrain ISCO size. We also demonstrate
that a convolutional neural network can be trained to predict ISCO size more
reliably than traditional approaches and can also recover source orientation
with high accuracy.
