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Paper: The Promise of Future VSOP-2 Observations for Studies of Helical Magnetic Fields and Their Evolution in Active Galactic Nuclei
Volume: 402, Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technologies
Page: 280
Authors: Mahmud, M.; Gabuzda, D.
Abstract: We present here results of an observational search for Faraday Rotation Measure (RM) gradients transverse to the VLBI jet direction in a sample of BL Lac objects that provide evidence for the presence of helical magnetic fields wrapped around the jets. This project has revealed new transverse RM gradients in several sources. In at least three sources, we observe new features, such as reversal of the transverse RM gradient with time or distance from the core. We discuss how these gradients could potentially be used to infer the intrinsic magnetic field configuration of the region surrounding the central black hole (e.g. dipolar, quadropolar; Blandford 2008). The use of 8 GHz VSOP-2 polarization observations in combination with ground VLBI polarization observations at higher frequencies will give us even higher angular resolution to probe in the central regions of the jet, enabling more accurate determination of the RM gradients on smaller scales, and could help identify possible counter-jets in some sources, which could provide a test for the magnetic field configuration of the black hole.
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