Abstract
Combined polarization imaging of radio jets from Active Galactic Nuclei (AGN) in circular and linear polarization, also known as full Stokes imaging, has the potential to constrain both the magnetic field structure and particle properties of jets. Although only a small fraction of the emission when detected, typically less than a few tenths of a percent but up to as much as a couple of percent in the strongest resolved sources, circular polarization directly probes the magnetic field and particles within the jet itself and is not expected to be modified by external screens. A key to using full Stokes observations to constrain jet properties is obtaining a better understanding of the emission of circular polarization, including its variability and spectrum. We discuss what we have learned so far from parsec scale monitoring observations in the MOJAVE program and from multi-frequency observations of selected AGN.
Highlights
Polarization observations of jets from Active Galactic Nuclei (AGN) in “full Stokes”, combining both linear and circular polarization, have the potential to address fundamental questions about their magnetic field structure and particle populations
Observational constraints on the full three-dimensional magnetic field structure on parsec-scales, near the jet origin in the super-massive black-hole/accretion disk system, are still ambiguous, indicating both that elements of large scale toroidal fields are present (e.g., [1,2,3,4]) and that shocks in the jet flow play an important role in the local field order (e.g., [5,6,7])
While circular polarization is clearly variable (e.g., [22,23]), there are indications that some sources may show a preferred sign of circular polarization at certain frequencies, e.g., [13,17,22], this has only been well established for Sgr A* [24,25]
Summary
While circular polarization is clearly variable (e.g., [22,23]), there are indications that some sources may show a preferred sign of circular polarization at certain frequencies, e.g., [13,17,22], this has only been well established for Sgr A* [24,25] In this proceedings, we first briefly review what is known about the emission mechanisms for circular polarization and discuss the prospects for better constraining the mechanism to answer fundamental questions about jet magnetic fields and particle populations. We focus on parsec-scale observations from the MOJAVE, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, program and share preliminary results from multi-epoch measurements of circular polarization in a large number of AGN jets
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