Observations of X-ray bursts by the 'Hakucho' satellite

Observational results on X-ray bursts obtained by the Japanese X-ray satellite are reviewed in conjunction with the general context of the neutron star model of the burst. Evidence indicates the existence of physically different kinds among type-I bursts which are widely believed to be from a thermonuclear flash occurring on the surface of a neutron star. There are cases which can not be accounted for by a simple nuclear flash model: The flash in a confined region of the surface and a change of the emitting area during the burst are suggested. Two type-I bursts were observed in succession within a short interval which was not of sufficient duration to accumulate the nuclear fuel for a flash. Coordinated optical/X-ray observations of bursts were performed. Optical bursts are tentatively interpreted in terms of the reprocessing of X-rays are at the accretion disk. The results will provide the basis for a discussion of the physical structure of the system. The evolution of the activity of type-II bursts from the rapid burster was observed from its onset for about two weeks and a novel mode of burst activity was discovered. (Auth.)