POLARIZED MID-INFRARED SYNCHROTRON EMISSION IN THE CORE OF CYGNUS A

We present high-angular (similar to 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% +/- 3% and 12% +/- 3% and a position angle of polarization of 27 degrees +/- 8 degrees and 35 +/- 8 in a 0 ''.38 (similar to 380 pc) aperture for each filter. The observed rising of the polarized flux density with increasing wavelength is consistent with synchrotron radiation from the parsec-scale jet close to the core of Cygnus A. Based on our polarization model, the synchrotron emission from the parsec-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.