2007ApJ...661...19P

X-ray and optical observations of quadruply lensed quasars can provide a microarcsecond probe of the lensed quasar, corresponding to scale sizes of ∼10²-10⁴ gravitational radii of the central black hole. This high angular resolution is achieved by taking advantage of microlensing by stars in the lensing galaxy. In this paper we use X-ray observations of 10 lensed quasars recorded with the Chandra X-Ray Observatory as well as corresponding optical data obtained with either the Hubble Space Telescope or ground-based optical telescopes. These are analyzed in a systematic and uniform way with emphasis on the flux ratio anomalies that are found relative to the predictions of smooth lens models. A comparison of the flux ratio anomalies between the X-ray and optical bands allows us to conclude that the optical emission regions of the lensed quasars are typically larger than expected from basic thin-disk models by factors of ∼3-30.