Refined modelling of the gravitationally lensed quasar PKS 1830-211

Abstract

PKS 1830-211 is a well studied radio-loud quasar with a flat spectrum undergoing strong gravitational lensing by a foreground galaxy. At cm-wavelengths the structure of PKS 1830-211 consists of two lensed images separated by 1 arcsecond and connected by an Einstein ring. High-resolution radio continuum observations have revealed structural changes in both the NE and the SW images. The absorption spectra arising from the foreground galaxy, at z = 0.89, show temporal variations. It is very likely that the variations in the lines of sight are related to changes in the structure of the background source. In this thesis we use a core-jet model of the background source and examine how variations in the illumination affect the absorption spectra. For this purpose, the lens system was divided into three parts: the source, the lens, and an absorption screen in the lens galaxy. The position of the jet was varied while keeping the lens and the absorption screen parameters constant. Temporal variations of the order of 1% in the absorption spectra over a time scale of 1 yr corresponding to a physical scale of about 0.3 pc, for a jet travelling at speed of light at the redshift of the source, could be reproduced with the model. This supports the claim that variations in the source structure can explain the observed temporal variations in the absorption spectra.