MILLIARCSECOND-SCALE POLARIZATION STRUCTURE IN THE QUASARS 3C-279 AND3C-454.3

Polarization-sensitive global VLBI observations at lambda = 6 cm of th e quasars 3C 279 and 3C 454.3 are presented; these observations offer resolution similar to 0.5 mas, corresponding to linear scales in the s ources similar to 2 pc. In both sources, the polarization associated w ith the jet emission indicates that the predominant jet magnetic field is longitudinal. In 3C 454,3, the magnetic field maintains alignment with the local jet direction even in places where the jet is highly cu rved. The degree of polarization in the jets ranges from 2 to 29 per c ent, and is typically similar to 15 to 20 per cent, indicating that th e jet components are optically thin. The core of 3C 279 is rather weak ly polarized (< 1.6 per cent), while that of 3C 454.3 is more strongly polarized (similar to 4.6 per cent), suggesting that 3C 454.3 may hav e been in the process of giving birth to a new VLBI component at the e poch of our observations. Both sources were imaged at epochs at which new components had recently emerged from the core. The magnetic field in the innermost knot in 3C 279 appears to be aligned with the local j et direction, as is typical of quasars, while that in the innermost kn ot in 3C 454.3 seems to be perpendicular to the local jet direction, s uggesting that this new component is associated with a transverse shoc k.