Observation of MXB1636-53 by HAKUCHO

The extended observation of the X-ray burster MXB1636-53 revealed that this burster exhibited a wide variety of profile from burst to burst. The peak luminosity of burst varied by the factor of 6. The X-ray energy flux, black-body temperature and the radius of radiation region were estimated under the assumption that the energy spectrum of X-ray burst fits to black-body radiation. The radius of black-body radiation is nearly the same for all bursts with largely different profile, peak luminosity and total energy. The constancy of the radius of generating region for all the bursts suggests that X-ray bursts are produced over the whole surface of a neutron star. The observed large fluctuation of the peak luminosity can not be satisfactorily explained by the current helium flash model. (Yoshimori, m.)