Submilliarcsecond Polarimetric Imaging of Blazar Jets at 43 GHz

Abstract

We present 43 GHz polarization images obtained with the Very Long Baseline Array of four blazars (0829+046, 1055+018, 1334-127, and AP Librae), as well as four active galactic nuclei, which served as polarization calibrators (DA 193, OJ 287, 3C 279, and 1611+343). Six of these objects are members of the Nartallo et al. millimeter-wave polarization blazar monitoring sample. We find no differences in the overall millimeter-wave polarization properties of the BL Lacertae objects and quasars in our sample. This is in contrast to previous findings at centimeter wavelengths, in which the inferred magnetic fields of quasars are found to be predominantly aligned with the jet, while perpendicular configurations are found in BL Lac objects. With the exception of 1611+343, a low optical polarization quasar, all of the unresolved blazar cores in our sample have inferred magnetic field orientations perpendicular to the inner jet direction. Past nonimaging millimeter-wave polarization monitoring data have shown that these core orientations are stable in three of our sample objects; this may be due to strong, unresolved standing shocks located very close to the base of the jet. We also detect in the jets of blazars a moderate-sized population of polarized components having electric vectors that lie at an oblique angle to the local jet direction. We find that the observed distribution of electric vector misalignment angles cannot be fitted by a single population of oblique shocks having arbitrary inclinations with respect to the jet axis. Such a population predicts an overabundance of shocks with electric polarization vectors aligned with the jet axis, produced by relativistic effects associated with the jet flow. We find the data to be more consistent with a scenario in which the polarized jet components are merely enhanced regions whose magnetic field orientations are controlled by some mechanism other than shocks.