Microlensing of nonsingular black holes at finite size: A ray tracing approach

We study the gravitational microlensing of various static and spherically symmetric nonsingular black holes (and horizonless, nonsingular compact objects of similar size). For pointlike sources we extend the parametrized post-Newtonian lensing framework to fourth order, whereas for extended sources we develop a ray tracing approach via a simple radiative transfer model. Modelling nonrelativistic proper motion of the lens in front of a background star we record the apparent brightness as a function of time, resulting in a photometric lightcurve. Taking the star radius to smaller values, our numerical results approach the theoretical predictions for pointlike sources. Compared to the Schwarzschild metric in an otherwise unmodified lensing geometry, we find that nonsingular black hole models (and their horizonless, nonsingular counterparts) both at finite size and for point lenses tend to feature larger magnifications in microlensing lightcurves.