Soft-spectrum gamma-ray bursts

A typical gamma to ray burst (GRB), when observed over the approximately 30 keV to 1 MeV range, has a 1 to 10 s duration and a spectrum describable in terms of a several-hundred-keV exponential function. However, KONUS data indicate that some GRBs may belong to a separate class of short (approximately 0.1 s), soft (kT 50 keV) events. This result has been questioned because the KONUS experiments, with only 4 s spectral time resolution and a lack of information approximately 30 keV, are not particularly well suited for the detection and study of these bursts. The UC Berkely/Los Alamos Solar X-Ray Spectrometer/GRB experiment on the International Cometry Explorer (ICE), with nearly continuous coverage of approxiomately one-sixth of the sky down to 5 keV at 0.5 s resolution, is better designed for such a task. Using ICE data, it was confirmed that soft-spectrum events do indeed exist, apparently with properties that set them apart from the general GRB population. Results from the ICE experiment are presented.