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Both the emission properties and evolution of Active Galactic Nuclei (AGN) radio jets are dependent on the magnetic (B) fields that thread them. Faraday Rotation measurements are a very important way of investigating these B fields, and can…

The presence of a helical magnetic field threading the jet of an Active Galactic Nucleus (AGN) should give rise to a gradient in the observed Faraday rotation measure (RM) across the jet, due to the associated systematic change in the…

Parsec-scale multi-wavelength VLBA polarization observations can be used to study the magnetic-field structures of Active Galactic Nuclei (AGN) based on Faraday Rotation (FR) gradients. A number of transverse FR gradients have been found,…

A number of groups have recently been active in searching for gradients in the ob- served Faraday rotation measure (RM) across jets of Active Galactic Nuclei (AGNs) on various scales and estimating their reliability. Such RM structures…

The idea that systematic Faraday Rotation gradients across the parsec-scale jets of AGNs can reveal the presence of helical magnetic (B) fields has been around since the early 1990s. These gradients are taken to be due to the systematic…

We are using "broadband" (4.6 to 43 GHz) multi-frequency VLBA polarization observations of compact AGN to investigate the 3-D structure of their jet magnetic (B) fields. Observing at several frequencies, separated by short and long…

Several multi-frequency polarization studies have shown the presence of systematic Faraday Rotation gradients across the parsec-scale jets of Active Galactic Nuclei (AGN), taken to be due to the systematic variation of the line-of-sight…

Radio interferometric observations of Active Galactic Nuclei (AGN) jets reveal the significant linear polarization of their synchrotron radiation that changes with frequency due to the Faraday rotation. It is generally assumed that such…

For the first time it has become possible to compare global 3D general relativistic magnetohydrodynamic (GRMHD) jet formation simulations directly to very-long baseline interferometric multi-frequency polarization observations of the…

We perform polarimetry analysis of 20 active galactic nuclei (AGN) jets using the Very Long Baseline Array (VLBA) at 1.4, 1.6, 2.2, 2.4, 4.6, 5.0, 8.1, 8.4, and 15.4 GHz. The study allowed us to investigate linearly polarized properties of…

Several multi-frequency polarization studies have shown the presence of systematic Faraday Rotation gradients across the parsec-scale jets of Active Galactic Nuclei (AGN), taken to be due to the systematic variation of the line-of-sight…

One possible origin for polarization structures across jets of Active Galactic Nuclei (AGNs) with a central "spine" of orthogonal magnetic field and a "sheath" of longitudinal magnetic field along one or both edges of the jet is the…

We investigate the emission properties that a large-scale helical magnetic field imprints on AGN jet synchrotron radiation. A cylindrically symmetric relativistic jet and large-scale helical magnetic field produce significant asymmetrical…

We present maps of the sign of the Faraday Rotation measure [sign(RM)] obtained from multi-frequency radio observations on the Very Long Baseline Array (VLBA). Many of the Active Galactic Nuclei (AGN) considered have B-field structures with…

The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic (B) field, which will give rise to a systematic…

Radio polarimetric observations of Active Galactic Nuclei can reveal the magnetic field structure in the parsec-scale jets of these sources. We have observed the gamma-ray blazar 3C 273 as part of our multi-frequency survey with the Very…

The formation of relativistic jets in active galactic nuclei (AGN) is related to accretion on to their central supermassive black holes, and magnetic fields are believed to play a central role in launching, collimating and accelerating the…

The magnetic field is believed to play a critical role in the bulk acceleration and propagation of jets produced in active galactic nuclei (AGN). Polarization observations of AGN jets provide valuable information about their magnetic…

Multi-frequency (4.6, 5, 5.5, 8, 8.8, 13, 15, 22 & 43 GHz) polarization observations of 6 "blazars" were obtained on the American Very Long Baseline Array (VLBA) over a 24-hr period on 2 July 2006. Observing at several frequencies,…

Motivated by recent observations that show increasing fractional linear polarization with increasing wavelength in a small number of optically thin jet features, i.e. "inverse depolarization", we present a physical model that can explain…