出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present results of intensity and linear polarization imaging and model fitting for two sources
based on VLBA observations for a sample of 1-Jy northern BL Lac objects. Observations were
carried out in August 2004 at 43, 22 and 15 GHz. The observed polarization vectors in the jets
are aligned with the jet, implying the presence of transverse magnetic fields. We confirm the
presence of a transverse Faraday rotation gradient across the jet of 1803+784, providing
evidence that this jet has a helical magnetic field.
