New rotation measures of distant pulsars in the inner Galaxy and magnetic field reversals

Abstract

We present new rotation measures (RMs) for 27 pulsars, most of which were discovered in searches by Clifton and Lyne and Clifton et al. These pulsars have generally high dispersion measures and low Galactic latitudes, and are located in the first quadrant of the Galaxy. The new RMs, considered together with existing RMs in the same directions, provide further evidence that the large-scale Galactic magnetic field along the Sagittarius arm is opposite in direction from the local field. We have run models used by Rand and Kulkarni, but with a more careful selection of the data, to find that the field changes direction at about 0.4 kpc inside the solar circle, locally points to Galactic longitude 88°, and has a strength of 1.4 μ, G. These RMs also provide evidence for a second reversal of the magnetic field direction in the inner Galaxy at a radius of 5.5 kpc, with a much stronger field beyond the reversal. The primary signature of this reversal is a systematic segregation of positive and negative RMs by distance and longitude in the region 0°</<40°, 3