Supernova remnant G292.2-0.5, its pulsar, and the Galactic magnetic field

The extended low-brightness Galactic radio source G292.2-0.5 is one of the few supernova remnants (SNRs) showing a likely association with a young pulsar. New observations of the remnant with the Australia Telescope Compact Array yield a distance of 8.4 kpc determined from HI absorption measurements, and the first detection of linear polarization. The polarization was studied at two frequencies near 5 GHz, revealing a high mean rotation measure, approximately +800 rad m(-2), strikingly similar to that of the pulsar. This similarity, and the compatibility of the pulsar distance estimate with the new SNR distance, now provides overwhelming evidence that the pulsar is indeed embedded within the SNR, and that both were presumably born in the same supernova event. The ratio of rotation measure to pulsar dispersion measure yields a value of -1.4 muG (towards us) for the (density-weighted) average line-of-sight component of magnetic field for the 8.4-kpc path-length to the SNR and pulsar. The unusually high rotation measure, together with the large distance over which it has accumulated, argues that this field is a persistent feature on a large scale that outweighs smaller-scale fluctuations and reversals. The 8.4-kpc path-length lies almost wholly within the Carina spiral arm of our Galaxy and thus this portion of the arm possesses an average clockwise field of 1.4 muG. We interpret other evidence to suggest that the clockwise field extends for at least a further 8.5 kpc along the same arm, in the region where it is usually referred to as the Sagittarius arm. Observations such as these provide a powerful tool for exploring the large-scale structure of the Galactic magnetic field in relation to the spiral-arm structure.