High rotation measure in the steep spectrum quasar 3C 147

We present VLBA polarimetric observations of the steep-spectrum quasar 3C 1 47 (0538+498) made at four frequencies in the available 5-GHz band, from wh ich we derived milliarcsecond-resolution images of the total intensity, pol arization, and rotation measure distributions. The jet extending to the sou thwest is followed out to a distance of about 200 mas from the core. The je t shows several gentle wiggles, and turns sharply toward the north near the end of its detected length. Polarization was detected in one bright featur e in the inner jet; the rotation measure of this feature (similar or equal to 1300 rad m(-2)) agrees with the known high rotation measure of the sourc e. The observations provide direct measurements of the rotation measure in the feature for which polarization was detected, making it possible to dero tate the observed polarization vectors to infer the underlying magnetic fie ld structure. This structure is roughly transverse to what appears to be th e dominant flow direction, suggesting that this bright feature is associate d with a relativistic shock.