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 HI observations from the Southern Galactic Plane Survey ofthe field around the anomalous X-ray pulsar 1E 1048.1-5937, a source whoseX-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 35x23 pc (for a distance of 2.7kpc) and an expansion velocity of approx 7.5 km/s. We interpret GSH288.3-0.5-28 as a wind bubble blown by a 30-40 M_sun star, but no such centralstar can be readily identified. We suggest that GSH 288.3-0.5-28 is the windbubble blown by the massive progenitor of 1E 1048.1-5937, and consequentlypropose that magnetars originate from more massive progenitors than do radiopulsars. This may be evidence that the initial spin period of a neutron star iscorrelated with the mass of its progenitor, and implies that the magnetar birthrate is only a small fraction of that for radio pulsars.Comment: 4 pages + 1 EPS figure, in emulateapj style. ApJ Letters, in pres