Micro-images of macro-lensed objects

Abstract

The study of gravitational micro-lensing at high optical depth has only rarely involved the close examination of the individual actual micro-images that arise as a result of the phenomenon. We discuss methods that refine on previous work done in the search for micro-images, which have been largely ignored in favor of other methods to study micro-lensing. With the help of magnification maps generated by Herr Prof. Dr. Joachim Wambsganss, we ran simulations that track positions and magnifications of micro-minima as functions of source position. We discuss the breakdown of a commonly used approximation for magnifications near fold caustics. Our results show that the approximation is noticeably broken at a caustic strength-scaled distance of 0.1. The relevance of this breakdown to work done by other authors is briefly examined. We then then discuss a few new results for the statistics of micro-images, deriving a formula for the mean micro-minimum magnification. We present a method for exactly calculating the caustic networks of micro-lensed systems, and calculate probability distributions for the caustic strength for two sets of parameters of interest. We present the creation of videos of the micro-lensing affect for pedagogical purposes. Finally, we briefly examine micro-lensing near macro-caustics and study the motion of micro-images as a point source crosses a macro-caustic.