An infrared ring around the magnetar SGR 1900+14

Magnetars: Ring of fire Magnetars are rotating neutron stars with magnetic fields at least an order of magnitude stronger than those of 'normal' radio pulsars. There are only about a dozen magnetars known to date and their evolutionary history is not yet firmly established. Circumstantial evidence links them to very massive stars as progenitors; now the discovery of an infrared ring or shell around magnetar SGR 1900+14 (a soft gamma repeater) confirms that link. Observations from the Spitzer telescope are consistent with the presence of a dust-free cavity in the magnetar environment — possibly produced by the giant flare emitted by the source in August 1998 — strongly suggesting an association with a cluster of massive stars. This paper reports the discovery of an infrared elliptical ring or shell surrounding the magnetar SGR 1900+14. It is suggested that a dust-free cavity was produced in the magnetar environment by the giant flare emitted by the source in August 1998 and concludes that SGR 1900+14 is unambiguously associated with a cluster of massive stars. Magnetars 1 , 2 are a special class of slowly rotating (period ∼5–12 s) neutron stars with extremely strong magnetic fields (>10 14 G)—at least an order of magnitude larger than those of the ‘normal’ radio pulsars. The potential evolutionary links and differences between these two types of object are still unknown; recent studies, however, have provided circumstantial evidence connecting magnetars with very massive progenitor stars 3 , 4 , 5 . Here we report the discovery of an infrared elliptical ring or shell surrounding the magnetar SGR 1900+14. The appearance and energetics of the ring are difficult to interpret within the framework of the progenitor’s stellar mass loss or the subsequent evolution of the supernova remnant. We suggest instead that a dust-free cavity was produced in the magnetar environment by the giant flare emitted by the source in August 1998. Considering the total energy released in the flare, the theoretical dust-destruction radius matches well with the observed dimensions of the ring. We conclude that SGR 1900+14 is unambiguously associated with a cluster of massive stars, thereby solidifying the link between magnetars and massive stars.