Radio-polarimetric observations of gravitational lenses

The goals of this thesis were to study the observational radio-polarimetric properties of gravitational lens systems. Such studies can constrain lensed source properties, propagation effects in the intervening lensing galaxies, and the general-relativistic invariance of polarization under lensing. We performed high dynamic-range VLBI imaging polarimetry of the gravitational lens system B0218+357 at 43 GHz, and further VLBI observations of this system in the frequency range 8 GHz - 43 GHz. Further analysis included a low-frequency VLA study of the gravitational lens system B0218+357 over the frequency range 330 MHz - 5 GHz. We also studied the VLA polarization morphology of a sample of gravitational lens systems over the frequency range 1.5 MHz - 43 GHz, and used contemporary algorithms to estimate rotation measure values of the lens sample. In addition, we proposed a framework for evaluating the performance of fringe-fit methods in the low SNR regime using bootstrap resampling. Our 43 GHz maps of B0218+357 provide the highest-resolution constraints on the detailed polarization morphology of the background source to date, confirm parity reversal in polarization structure predicted by gravitational lensing theory, and verify the invariance of polarization properties under gravitational lensing. We present absolute rotation measures, lensing galaxy magnetic field estimates, and the fractional linear polarization distribution for our lensing population sample. We propose a new explanation for the earlier puzzling radial polarization structure in the Einstein ring in B0218+357. In closing, we verify that bootstrap resampling is an effective framework for assessing the performance of fringe-fitting estimators as needed in millimeter-wavelength VLBI