AAS 197, January 2001
Session 39. Polarimetry and Variability in AGN
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

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[39.05] Optical-IR Polarimetry of the Blazar 3C\,273: Orthogonal Synchrotron Components during a Flare

B. J. Wills, L. L. Cross (Univ. Texas), J. H. Hough (Univ. Hertfordshire), J. A. Bailey (AAO), D. Wills (Univ.Texas)

3C\,273 usually exhibits low optical polarization, \lesssim0.5% and up to nearly 2% during outburst. We caught it in a more active phase. We present UBVRIJHKL^{\prime} polarization and flux density measurements of 3C\,273 over >8 days during the 1988 February flare. The complex 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 approximately orthogonal wavelength-independent polarization position angles. The steeper component shows polarization approximately transverse to the projected VLBI jet direction. The variations in polarized flux-density, spectral index and position angle, account for the observed night-to-night variability, and track each other with no discernable time-lag. These results suggest an origin in two nearly co-spatial components, the flatter spectrum one arising in the compressed magnetic field of a transverse shock, and the other arising 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\prime band (3.8\mum). 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.

We thank the staff of UKIRT and McDonald observatories for observational support, and the PATT for the allocation of telescope time. The research at Univ. Texas was supported by NASA LTSA grant number NAG5-3431 to B.J.W.

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