A FAINT POLARIZED ARC NEAR THE SUPERNOVA REMNANT MSH-15-52 (G-320.4-1.2)

The Galactic radio source MSH 15-52 (G 320.4 - 1.2) is a 30-arcmin non-thermal complex associated with the optical nebula RCW 89 and believed to be the remnant of a supernova; it contains the X-ray and radio pulsar PSR 1509 - 58, and it is assumed that an association with the SNR exists. In this paper we present a radio polarization study of this region which shows the presence of a polarized ring or shell, approximately 40 arcmin in diameter, either extending from G 320.4 - 1.2 or coincident with part of it. The distributions of Faraday rotation and depolarization are also presented for this region. While G 320.4 - 1.2 clearly has a radial projected magnetic field, the field in the large ring is tangential, which suggests that it may be a blow-out from G 320.4 - 1.4. An alternative interpretation is that this new feature is a separate supernova remnant, G 320.6 - 1.6.