MaB$μ$lS-2: high-precision microlensing modelling for the large-scale survey era

Abstract

Galactic microlensing datasets now comprise in excess of $10^4$ events, and with the advent of next generation microlensing surveys that may be undertaken with facilities such as the Rubin Observatory (formerly LSST) and Roman Space Telescope (formerly WFIRST), this number will increase significantly. So too will the fraction of events with measurable higher order information such as finite source effects and lens-source relative proper motion. Analysing such data requires a more sophisticated Galactic microlens modeling approach. We present a new second-generation Manchester-Besançon Microlensing Simulator (MaB$μ$lS-2), which uses a version of the Besançon population synthesis Galactic model that provides good agreement with stellar kinematics observed by HST towards the bulge. MaB$μ$lS-2 provides high-fidelity signal-to-noise limited maps of the microlensing optical depth, rate and average timescale towards a 400 sq. degree region of the Galactic bulge in several optical to near-infrared pass-bands. The maps take full account of the unresolved stellar background as well as limb-darkened source profiles. Comparing MaB$μ$lS-2 to the efficiency-corrected OGLE-IV 8,000 event sample shows a much improved agreement over the previous version of MaB$μ$lS, and succeeds in matching even small-scale structural features in the OGLE-IV event rate map. However, there remains evidence for a small under-prediction in the event rate per source and over-prediction in timescale. MaB$μ$lS-2 is available online ( ) to provide on-the-fly maps for user supplied cuts in survey magnitude, event timescale and relative proper motion.