Polarized Mid-Infrared Synchrotron Emission in the Core of Cygnus A
  We present high-angular (~0.4") resolution mid-infrared (MIR) polarimetric
observations in the 8.7 ${\mu}$m and 11.6 ${\mu}$m filters of Cygnus A using
CanariCam on the 10.4-m Gran Telescopio CANARIAS. A highly polarized nucleus is
observed with a degree of polarization of 11${\pm}$3% and 12${\pm}$3% and
position angle of polarization of 27${\pm}$8 degrees and 35${\pm}$8 degrees in
a 0.38" (~380 pc) aperture for each filter. The observed rising of the
polarized flux density with increasing wavelength is consistent with
synchrotron radiation from the pc-scale jet close to the core of Cygnus A.
Based on our polarization model, the synchrotron emission from the pc-scale jet
is estimated to be 14% and 17% of the total flux density in the 8.7 ${\mu}$m
and 11.6 ${\mu}$m filters, respectively. A blackbody component with a
characteristic temperature of 220 K accounts for >75% of the observed MIR total
flux density. The blackbody emission arises from a combination of (1) dust
emission in the torus; and (2) diffuse dust emission around the nuclear region,
but the contributions of the two components cannot be well constrained in these
observations.
