SNR G320.4-01.2 and PSR B1509-58: New radio observations of a complex interacting system

We describe radio continuum and spectral line observations of the source G320.4-01.2 (MSH 15-52) and the coincident young pulsar B1509-58 made with the Australia Telescope Compact Array. Based on a comparison between X-ray and radio observations, we argue that the two main radio components of G320.4-01.2 are a single supernova remnant (SNR), which HI absorption indicates is at a distance of 5.2+/-1.4 kpc. A high-resolution correspondence between radio and X-rays argues that the pulsar is interacting with the SNR via an opposed pair of collimated outflows. The outflow itself is seen as an elongated X-ray feature surrounded by a highly polarized radio sheath, while the interaction with the SNR manifests itself as a ring of radio/X-ray knots within the optical nebula RCW 89. We reject the hypothesis that the pulsar outflow powers the entire RCW 89 region. SNR G320.4-01.2 and PSR B1509-58 agree in distance and in rotation measure, and appear to be interacting. We thus conclude that the two objects are associated and have an age of <~1700 yr. We propose that the SNR resulted from a high-energy or low-mass supernova which occurred near the edge of an elongated cavity. Such a model can account for the SNR's bilateral appearance, its large apparent age, the significant offset of the pulsar from the SNR's centre and the faintness of the pulsar-powered nebula at radio wavelengths.