Variability of the centimeter-submillimeter spectrum and polarization of 3C 273 during outburst

Centimeter to submillimeter total flux and polarization monitoring data are used to investigate the nature of a prominent flare in the quasar 3C 273 d uring 1995/6. After removal of the quiescent level, the resulting "flare sp ectra" are well fitted by a simple homogeneous synchrotron source model, wh ich in turn allows the movement of the self-absorption turnover to be track ed during the flare. Both the flare amplitude/time delay relationship and t he overall spectral evolution are qualitatively consistent with existing mo dels. The early evolution of the spectrum is best determined and is shown t o be in excellent agreement with the Compton stage of the Marscher & Gear s hock model. However, the polarization behavior during the flare is differen t at millimeter and centimeter wavelengths and the observations are difficu lt to reconcile with a simple transverse shock. They are, however, consiste nt with a conical shock for which the observed polarization properties vary with distance along the jet. Such variations may be caused, for example, b y a change in cone angle owing to disruption caused by the growing componen t of the magnetic field parallel to the jet axis or by a moderate change in viewing angle.