Friday 16 March at 2:30pm

ABSTRACT: "3C 273 usually exhibits low optical polarization, <~0.5% and up to nearly 2% during outburst. We caught it in a more active phase during a HATPOL run at UKIRT, following UBVRIJHKL' polarization and flux density over >8 days in 1988 February. The complicated polarization wavelength-dependence and its night-to-night variation are well described by the combination of two simple synchrotron spectra, with power-law polarized flux-density and polarization position angles perpendicular and parallel to 3C 273's famous multiwavelength jet. The variations in polarized flux-density, spectral index and position angle track each other with no discernable time-lag. We suggest that the flatter spectrum component arises in the compressed magnetic field of a transverse shock, and the other from electrons accelerated just outside the shocked region where the dominant magnetic field is parallel to the jet. "The highest measured polarization was 4.0 +/- 0.5% in L' band (3.8um). The largest polarization that would have been observed in the presence of just the strongest synchrotron component (i.e., no cancellation of polarization) was 6.4% (H-band). This would put 3C 273 clearly in the blazar category."