Unusual Burst Emission from the New Soft Gamma Repeater SGR 1627−41

Abstract

In 1998 June-July, the Konus-Wind burst spectrometer observed a series of bursts from the new soft gamma repeater SGR 1627-41. Time histories and energy spectra of the bursts have been studied, revealing fluences and peak fluxes in the ranges 3 × 10-7 to 7.5 × 10-6 ergs cm-2 and 10-5 to 10-4 ergs cm-2 s-1, respectively. One event, 18 June 6153.5 s UT, stands out dramatically from this series. Its fluence is ∼7 × 10-4 ergs cm-2, and its peak flux is ∼2 × 10-2 ergs cm-2 s-1. These values from a source at a distance of 5.8 kpc yield an energy output of ∼3 × 1042 ergs and a maximum luminosity of ∼8 × 1043 ergs s-1 for isotropic emission, similar to the values for the famous 1979 March 5 and 1998 August 27 events. In terms of energy, this event is another giant outburst seen in a third soft gamma repeater! However, this very energetic burst differs significantly from the other giant outbursts. It exhibits no separate initial pulse with a fast rise time, no extended tail, and no pulsations. It is rather similar to ordinary repeated bursts, but is a few hundred times stronger in intensity. According to the magnetar model by Thompson & Duncan, such a burst may be initiated by a strong starquake when a crust fracture propagates over the whole surface of a neutron star.