Quasar Microlensing, Timo Anguita (DAA-PUC)

The images of most gravitationally lensed quasars are subject to temporal brightness variations due to microlensing by stars in their lensing galaxies. These brightness variations result in discrepancies between the observed flux ratios among lensed images and the expectations from simple theoretical models, or "flux ratio anomalies". In this talk, after a brief quasar lensing 

introduction, I will show the observational signatures of the quasar microlensing phenomenon, and how these can allow to distinguish it from other effects responsible for inducing flux ratio anomalies. I will present the use of microlensing as tool to probe for the inner structure of quasars using the quadruple quasar Q2237+0305 as a working example. By studying the microlensing induced photometric variability in image C of the system during the year 1999 we have obtained constraints on the accretion disk structure of the background quasar.