N. Kawai, M. Matsuoka, H. Inoue, Y. Ogawara, Y. Tanaka, H. Kunieda, and Y. Tawara
The Rapid Burster (MXB1730-335) was observed from the X-ray astronomy satellite Tenma in August 1983 and July 1984. The spectra of both type I and type II bursts are well described by blackbody spectra with a slight excess above 10 keV. The emission region of type II bursts at the peak is found to be significantly larger than that of type I bursts, suggesting the presence of an optically-thick emission region larger than the neutron star. The spectral evolution associated with the time-scale invariant profile in the decay of most type II bursts is studied. Although most of the variation in X-ray flux within a type II burst is attributed to variation in the emission area, the temperature is also found to be variable. The variation in the color temperature of type II bursts is also time scale invariant. These observational results suggest the presence of a regulation mechanism for the accretion process, in addition to the reservoir required from the E-Delta t relation. A possible picture of the generation mechanism of the type II bursts is discussed based on these observations.