A stellar wind bubble coincident with the anomalous X-ray pulsar 1E 1048.1-5937: Are magnetars formed from massive progenitors?

We present 21 cm H I observations from the Southern Galactic Plane Survey of the field around the anomalous X-ray pulsar 1E 1048.1 - 5937, a source whose X-ray properties imply that it is a highly magnetized neutron star ( a "magnetar"). These data reveal an expanding hydrogen shell, GSH 288.3 - 0.5 - 28, centered on 1E 1048.1 - 5937, with a diameter of 35 x 23 pc (for a distance of 2.7 kpc) and an expansion velocity of approximate to7.5 km s(-1). We interpret GSH 288.3 - 0.5 - 28 as a wind bubble blown by a 30-40 M-. star, but no such central star can be readily identified. We suggest that GSH 288.3 - 0.5 - 28 is the wind bubble blown by the massive progenitor of 1E 1048.1 - 5937 and consequently propose that magnetars originate from more massive progenitors than do radio pulsars. This may be evidence that the initial spin period of a neutron star is correlated with the mass of its progenitor and implies that the magnetar birthrate is only a small fraction of that for radio pulsars.