2022A&A...665A.127D

We present a fast algorithm aimed at reproducing the light curves of distant stars undergoing microlensing near critical curves. The need for these type of algorithms has been motivated by recent observations of microlensing events of distant stars at high redshift and involving extreme magnification factors. The algorithm relies on a low-resolution computation of the deflection field due to an ensemble of microlenses near critical curves and takes advantage of the gradually varying nature of the deflection field to infer the magnification of the unresolved images. The algorithm is capable of resolving microlenses at cosmological distances with planet-sized masses, as well as typical background luminous stars of a few solar radii. Using this algorithm, light curves covering decades of relative motion between the source and the web of microcaustics, at nanoarcsec resolution, can be reproduced within a matter of minutes on a basic laptop. Classic inverse ray tracing simulations at the same resolution would take days or weeks to produce, consuming massive computational resources.