A ROBUST DETERMINATION OF THE SIZE OF QUASAR ACCRETION DISKS USING GRAVITATIONAL MICROLENSING

Abstract

Using microlensing measurements from a sample of 27 image-pairs of 19 lensed\nquasars we determine a maximum likelihood estimate for the accretion disk size\nof an {{\\em}average} quasar of $r_s=4.0^{+2.4}_{-3.1} $ light days at rest\nframe $<\\lambda>=1736$\\AA\\ for microlenses with a mean mass of\n$<M>=0.3M_\\odot$. This value, in good agreement with previous results from\nsmaller samples, is roughly a factor of 5 greater than the predictions of the\nstandard thin disk model. The individual size estimates for the 19 quasars in\nour sample are also in excellent agreement with the results of the joint\nmaximum likelihood analysis.\n