Magnifications of paired micro-images emerging from a micro-lensing critical curve

Abstract Studies of the inner regions of micro-lensed active galactic nucleus during caustic crossing events have often relied upon the approximation that the magnification near a fold caustic is inversely proportional to the square root of the source-caustic distance. We examine here the behaviour of the individual micro-images (one a micro-minimum of the light traveltime, the other a micro-saddle) that emerge as a point source crosses a micro-fold caustic. We provide a variety of statistics on both the behaviour of the two newly created micro-images and some parameters that appear in higher order approximations for the magnification. We compare the predictions of these higher order approximations to the actual image magnifications of our simulations.

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