Size is everything : universal features of quasar microlensing with extended sources

Abstract

We examine the effect that the shape of the source brightness profile has on the magnitude fluctuations of images in lens systems due to microlensing. We do this by convolving a variety of accretion disk models (including Gaussian disks, uniform disks, "cones," and a Shakura-Sunyaev thermal model) with two magnification patterns in the source plane, one with convergence [kappa] = 0.4 and shear [gamma] = 0 (positive parity), and the other with [kappa]=[gamma]= 0.6 (negative parity). By looking at magnification histograms of the convolutions and using chi-squared tests to determine the number of observations that would be necessary to distinguish histograms associated with different disk models, we find that, for circular disk models, the microlensing fluctuations are relatively insensitive to all properties of the models except the half-light radius of the disk.