PAGaN I: Multi-Frequency Polarimetry of AGN Jets with KVN
  Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to
study the structure of and physical conditions in relativistic outflows. For
such studies, multi-frequency polarimetric very long baseline interferometric
(VLBI) observations are important as they directly probe particle densities,
magnetic field geometries, and several other parameters. We present results
from first-epoch data obtained by the Korean VLBI Network (KVN) within the
frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We
observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129
GHz in dual polarization mode. Our observations constrain apparent brightness
temperatures of jet components and radio cores in our sample to $>10^{8.01}$ K
and $>10^{9.86}$ K, respectively. Degrees of linear polarization $m_{L}$ are
relatively low overall: less than 10%. This indicates suppression of
polarization by strong turbulence in the jets. We found an exceptionally high
degree of polarization in a jet component of BL Lac at 43 GHz, with $m_{L}
\sim$ 40%. Assuming a transverse shock front propagating downstream along the
jet, the shock front being almost parallel to the line of sight can explain the
high degree of polarization.
