The University of Michigan Centimeter-Band All Stokes Blazar Monitoring Program: Single-Dish Polarimetry as a Probe of Parsec-Scale Magnetic Fields

摘要

The University of Michigan 26-m paraboloid was dedicated to obtaining linearpolarization and total flux density observations of blazars from the mid-1960suntil June 2012 providing an unprecedented record tracking centimeter-bandvariability over decades at 14.5, 8.0, and 4.8 GHz for both targeted objectsand members of flux-limited samples. In the mid-1970s through the mid-1980s,and during the last decade of the program, observations were additionallyobtained of circular polarization for a small sample of radio-bright (S>5Jy),active sources. Key program results include evidence supporting class-dependentdifferences in the magnetic field geometry of BL Lac and QSO jets,identification of linear polarization changes temporally associated with fluxoutbursts supporting a shock-in-jet scenario, and determination of the spectralevolution of the Stokes V amplitude and polarity for testing proposed models.Recent radiative transfer modeling during large flares supports a jet scenariowith a kinetically-dominated, relativistic flow at parsec scales with embeddedturbulent magnetic fields and dynamically-weak ordered components which may behelical; the circular polarization observations are consistent withlinear-to-circular mode conversion within this turbulent jet environment.