The Interstellar Medium around the Supernova Remnant G320.4-1.2

Abstract

Using the Australia Telescope Compact Array, we have carried out a survey of the H I emission in the direction of the barrel-shaped supernova remnant (SNR) G320.4-1.2 (MSH 15-52) and its associated young pulsar B1509-58. The angular resolution of the data is 4farcm0 × 2farcm7, and the rms noise is of order 30 mJy beam-1 (~0.5 K). The H I observations indicate that the north-northwest radio limb has encountered a dense H I filament (density ~12 cm-3) at the same LSR velocity as that of the SNR (VLSR ~ -68 km s-1). This H I concentration would be responsible for the flattened shape of the northwestern lobe of G320.4-1.2 and for the formation of the radio-optical–X-ray nebula RCW 89. The emission associated with the bright knots in the interior of RCW 89 can be explained as arising from the interaction between the collimated relativistic outflow from the pulsar and the denser part of this H I filament (density ~15 cm-3). The south-southeastern half of the SNR, on the other hand, seems to have rapidly expanded across a lower density environment (density ~0.4 cm-3). The H I data also reveal an unusual H I feature aligned with a collimated outflow generated by the pulsar, suggestive of association with the SNR. The anomalous kinematical velocity of this feature (VLSR ~ 15 km s-1), however, is difficult to explain.