Gravitational Mapping of a Quasar Disk

Abstract

Since the radiation from different portions in the central region of a quasar can be successively amplified during a microlensing event, microlensing light curves provide us with fruitful information regarding the emissivity distribution of an accretion disk located at the quasar center. We present a basic methodology how to map the emissivity distribution of the disk as a function of the radial distance from the center, $Q(r)$, from `observed' microlens light curves during a caustic crossing event. Our proposed method is based on the standard inversion technique, the so-called regularization method, and the Abel's transformation of the one-dimensional luminosity profile integrated along the line parallel to the caustics. The technique will be used to map the disk structure in Q2237+0305, for which the HST and AXAF observations are scheduled. A reconstruction of the image on length scales of several to ten AUs is quite feasible for this source, as long as measuring errors are within 0.02 mag and the observation time intervals are a week or less.