The most recent results of GRB observations with Ginga

Abstract

Since the launch of Ginga in 1987, we have detected more than 80 gamma-ray bursts (GRBs) up to the end of October 1990. At least three GRBs among them have shown the cyclotron spectral feature in their burst spectrum. These spectral features strongly suggest neutron stars with strong magnetic fields as a possible origin of GRBs. Of the many GRBs detected with Ginga we have noticed a peculiar characteristic in one GRB, GB900126, which showed X-ray precursor emission with a time scale of 10 s before the first onset of gamma-ray photons. The spectrum of the precursor was very soft and looks like a thermal spectrum in origin. We discuss these results in the framework of a possible origin of neutron stars. These observations were done by an international collaboration between LANL in the USA and ISAS, Japan.