Cenacchi, Elena (2009) Full Stokes polarimetry with the Effelsberg 100-m radio telescope. PhD thesis, Universität zu Köln.
The first part of this thesis is dedicated to the development of a new calibration procedure that allows full Stokes measurements with the Effelsberg antenna. After introducing some basic concepts and definitions of polarimetry (Ch. 2), we have studied in detail the instrumental noise that a single-dish radio telescope adds to the polarimetric signal once this has been received (Ch. 3), analysing each part of the receiving chain. Focusing on the aberration introduced by the most common radioastronomical receiver, we have derived the degradation in its mathematical formalism, computing the instrumental Müller matrix of the telescope, in order to derive the corrections to be applied to recover the original information carried out by the signal, along with the treatment of the errors during the process (Ch. 4). The theoretical study of the full Stokes calibration has been followed by a 1-year test phase, carried out with the 5 GHz receiver (one of the most accurate available at Effelsberg). The results of the test phase, along with the comparison of our results with those obtained by the 26-m telescope of the University of Michigan (the only one single-dish telescope that carried out circular polarization measurements, before this PhD work) are presented in Ch. 5. The second part is dedicated to the full polarimetric survey carried out by the Effelsberg and Westerbork telescopes on 257 sources from the 1-Jy catalogue at 5 GHz. The technical characteristics of the survey are presented in Ch. 6. Once we have completed the data calibration for all the measurements (the complete results are listed in Appendix A), we have carried out some statistical tests, aimed to describe the behaviour of circular polarization according to the main source properties (optical classification, redshift, linear polarization, two-point spectral index, see Ch. 7). Finally, we have extended the calibration procedure to more frequencies, acquiring, for the first time at Effelsberg, the full Stokes spectra of a sample of sources, that appeared circularly polarized from the 5 GHz survey. The spectra are included in Appendix B for future reference. Ch. 8 contains the first results obtained from the comparison of the observed spectra with the theoretical ones, giving an outlook of the possible scientific results achievable with this new technique.
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