Full Polarization Spectra of 3C 279
  We report the results of parsec-scale, multi-frequency VLBA observations of
the core region of 3C 279 in Stokes I, linear polarization, and circular
polarization. These full polarization spectra are modeled by radiative transfer
simulations to constrain the magnetic field and particle properties of the
parsec-scale jet in 3C 279. The polarization properties of the core region,
including the amount of linear polarization, the amount and sign of Faraday
rotation, and the amount and sign of circular polarization can be explained by
a consistent physical picture. The base of the jet is modeled as an
inhomogeneous Blandford-Konigl style conical jet dominated by a vector-ordered
poloidal magnetic field along the jet axis, and we estimate its net magnetic
flux. This poloidal field is responsible for the linear and circular
polarization from this inhomogeneous component. Farther down the jet the
magnetic field in two homogeneous features is dominated by local shocks and a
smaller fraction of vector-ordered poloidal field remains along the jet axis.
In this picture, we find the jet to be kinetically dominated by protons with
the radiating particles being dominated by electrons at an approximate fraction
of >~ 75%. Based on the amounts of Faraday conversion deduced for the
homogeneous components, we find a plausible range for the lower cutoff in the
relativistic particle energy spectrum to be 5 <~ gamma_l <~ 35. The physical
picture described here is not unique if the observed Faraday rotation and
depolarization occur in screens external to the jet; however, we find the joint
explanation of linear and circular polarization observations from a single set
of magnetic fields and particle properties internal to the jet to be compelling
evidence for this picture. (Abridged)
