Pulsar rotation measures and the magnetic structure of our Galaxy

Abstract

We have obtained 63 rotation measures (RMs) from polarization observations of southern pulsars, of which 54 are new measurements and three are varied from previous values. The new pulsar RM data at high Galactic latitudes are mostly consistent with the antisymmetric RM distribution found previously. For the Galactic disc, evidence for a field reversal near the Perseus arm, and possibly another beyond it, is presented. Inside the Solar Circle, in addition to the two known field reversals in or near the Carina—Sagittarius arm and the Crux—Scutum arm, a further reversal in the Norma arm is tentatively identified. These reversals, together with the pitch angle derived from pulsar RM and stellar polarization distributions, are consistent with bisymmetric spiral models for the large-scale magnetic field structure in the disc of our Galaxy. However, discrimination between models is complicated by the presence of smaller scale irregularities in the magnetic field, as well as uncertainties in the theoretical modelling.