The parsec-scale polarization structure of nine BL Lacertae objects at lambda=3.6 cm

Polarization-sensitive lambda = 3.6 cm global VLBI images of the BL Lacertae objects 0235+164, 0454+844, 0735+178, OJ 287, 0954+658, 1219+285, 1803+784, 1823+568 and BLLac at epoch 1990.47 are presented. 6-cm VLBI polarization observations of BL Lacertae objects have revealed surprisingly characteristic and distinctive polarization structure, suggesting that relativistic shocks are common in the VLBI jets of these sources. These first 3.6-cm images also point toward the common presence of relativistic shocks, but indicate that the dominant magnetic field in jet components may occasionally be longitudinal. They also indicate the presence of possible interknot polarization associated with an underlying longitudinal magnetic field. The core polarizations observed at 3.6 cm tend to be lower than those observed at 6 cm, providing evidence that the higher 6-cm core polarizations are due to substantially polarized emerging knots that are blended with the cores.