Minilensing of multiply imaged quasars: flux variations and vanishing of images

The gravitational influence of minilenses which are located in lens galaxies and clusters and which intercept the light paths from multiply imaged quasars is investigated by developing an analytical framework. The mathematical formulation is adopted for deriving flux variations due to minilensing, and explicit light curves are computed numerically for a variety of minilens paths coming close to the images of the twin quasar 0957 + 561 A, B. It is demonstrated that under certain circumstances the operation of minilensing can lead to the vanishing of an image. This feature could provide a diagnostic probe of quasar structure and dark matter in the lenses and also serve as a test of gravitational lens models.