X-ray and optical flux ratio anomalies in quadruply lensed quasars. I. Zooming in on quasar emission regions

X- ray and optical observations of quadruply lensed quasars can provide a microarcsecond probe of the lensed quasar, corresponding to scale sizes of similar to 10(2 -) 10(4) 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 similar to 3-30.