Association of PSR0740-28 with an H I shell in Puppis

During a survey of the interstellar atomic hydrogen (H I ) distribution in the Puppis region of the Milky Way, we detected numerous, sometimes expanding, H I shells and filaments, indicative of past energetic explosive events in this area of the Galaxy. One of these shells, GS241–01 + 15, appears to be physically associated with the young pulsar PSR0740–28. In particular, the pulsar is coincident in position with an H I hotspot on the rim of the shell, and there are two nearby non-thermal radio sources, one of which lies on the rim of the H I shell coincident with the position of the open cluster Hfl l, the other lying near the centre of the shell. Both non-thermal sources have been previously identified as possible supernova remnants (SNRs) 1,2 . Furthermore, velocity measurements of the peak emission from the hydrogen shell and of the 21-cm absorption spectrum of the pulsar offer strong confirmation that the pulsar and the H I shell lie at the same distance from the Sun. This result is of interest because very few pulsars have been linked to known supernova remnants, and only the Crab and Vela pulsars with any degree of certainty 3 . Whether the pulsar PSR0740–28 is the remnant of the supernova progenitor of the H I ring, or perhaps the remnant of an early supernova in a young stellar group which was formed by the expanding H I shell, is as yet unclear. Present data seem to support the latter interpretation, suggesting that PSR0740–28 may have resulted from a ‘second-generation’ supernova event.