Physics
Scientific paper
Aug 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990stin...9222300w&link_type=abstract
Thesis Ludwig-Maximilians-Univ., Munich (Germany, F.R.). Fakultaet für Physik.
Physics
1
Gravitational Effects, Lenses, Light Curve, Magnification, Stellar Radiation, Beams (Radiation), Emission Spectra, Light Emission, Line Spectra, Quasars
Scientific paper
The phenomenon of gravitational microlensing, the gravitational lens effect of individual stars inside a lensing galaxy on the light rays of a background quasar, is investigated. The basics of gravitational lensing are given, and the current state-of-the-art in observations as well as in theory is summed up. The method used for the simulation of the gavitational light deflection is based on a hierarchical tree code which is optimized for the application in gravitational lensing, so almost one million individual stars could be used in the calculations. In addition to the standard ways of analysis, like magnification patterns, light curves, and magnification probabilities, the concept of percolation is applied to the resulting two-dimensional magnification distributions, as well as that of the fractal dimension of minimal spanning clusters. A large variety of numerical simulations is presented. Microlensing at (macro)caustics is investigated, and the large variety in morphology of gravitationally lensed images, which consist of very many micro-images, is shown. As an application, a microlensing model for image A of the quadruple quasar 2237+0305 is developed. Features in the resulting light curve similar to the one observed are easily reproduced, and typical time scales for the frequency of such events are determined. The effect of microlensing on broad emission lines of quasars is explored. In contrast to common wisdom it is found that microlensing can influence such emission lines: in the spectra of different images of a multiple quasar, a broad emission line should show different profiles due to the fact that the light has traversed different regions, and, thus, different star fields of the lensing galaxy.
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