Gravitational Micro-Lensing as a Clue to Quasar Structure

Abstract

We discuss the possibilities of determining the one-dimensional intrinsic luminosity profile of a quasar which is affected by gravitational micro-lensing (lensing of stars in a distant galaxy). When the source crosses a critical curve (Jacobian of the lens mapping vanishes, i.e. anti-caustic) due to relative transverse motion, a typical asymmetric peak occurs in the lightcurve, a so-called high amplification event (HAE). It corresponds to the appearance (or disappearance) of two bright micro-images with a separation of some microarcseconds, which is not resolvable. However the brightness changes during a HAE are easily observable. Since it is an eclipse-like effect, it gives the possibility of calculating the one-dimensional source profile from the lightcurve. We present the method and discuss the results of its application on simulated lightcurves. It should be possible to obtain information on the structure of quasars on a scale smaller than o.ool pc for solar mass stars.