Hard burst emission from the soft gamma repeater SGR 1900+14

We present evidence for burst emission from SGR 1900+14 with a power-law hi gh-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these e missions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ra y burst (GRB) function rather than by the traditional optically thin therma l bremsstrahlung model. We find that the spectral evolution within these ha rd events obeys a hardness/intensity anticorrelation. Temporally, these eve nts are distinct from typical SGR burst emissions in that they are longer ( similar to 1 s) and have relatively smooth profiles. Despite a difference i n peak luminosity of greater than or similar to 10(11) between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and sp ectral similarities between the two kinds of bursts, aside from spectral ev olution. We outline an interpretation of these events in the context of the magnetar model.