Astrophysical Applications of Gravitational Micro-Lensing

Abstract

Gravitational micro-lensing due to stars in the deflecting galaxy influences the brightness and the spectra of the macro-images. Thus differences in the spectra of different macro-images are not automatically an argument against gravitational lensing. Furthermore changes in the spectra due to micro-lensing may give informations on the quasar structure. From high amplification events the brightness profile of the source may be obtained. The time scale of the high amplification event is proportional to the source radius and inverse proportional to the transversal velocity. Due to the large brightness gradient by a high amplification event, a “parallax-effect” occurs, from which the transversal velocity may be obtained, and thereby the source radius (R=Δ t · VT). We roughly estimate 0.3 high amplication events per year for all gravitationally lensed quasars. Frequent monitoring should be carried out in order to predict high amplification events as early as possible.