RXTE observations of 4U 1630-47 during the peak of its 1998 outburst

We present an analysis of the RXTE observations of 4U 1630-47 during its 1998 outburst. The light curve and the spectral evolution of the outburst were significantly different from the outbursts of the same source in 1996 and 1999. Special emphasis was placed on observations taken during the initial rise and during the maximum of the outburst. The maximum of the outburst was divided into three plateaux, with almost constant flux within each plateau, and fast jumps between them. The spectral and timing parameters are stable for each individual plateau, but significantly different between the plateaux, The variability detected on the first plateau is of special interest. During these observations the source exhibits quasi-regular oscillations with a period of similar to 10-20 s. Our analysis revealed a difference in temporal behaviour of the source at high and low fluxes during this period of time. The source behaviour can be generally explained in the framework of the two-phase model of accretion flow, involving a hot inner Comptonization region and surrounding optically thick disc. The variability and spectral evolution of the source were similar to what was observed earlier for other X-ray novae. We show that 4U 1630-47 resembles, in several aspects, other transient and persistent black hole binaries.