1998A&A...340..431O

We report results of five pointed BeppoSAX observations of the black hole candidate 4U 1630-47 during part of its 1998 outburst when the 2-10keV source luminosity decreased from 2.1x10³⁸erg/s (for an assumed distance of 10kpc) by a factor of ∼7. The 2-200keV spectrum can be modeled by a soft multi-temperature disk blackbody and a hard power-law. During four of the observations, there is evidence for deviations from a pure power-law shape >20keV which may be due to reflection. As the outburst decayed a number of spectral trends are evident: (1) the amount of photoelectric absorption decreased, (2) the spectrum became harder (i.e. the power-law index became smaller), (3) the temperature of the disk blackbody decreased and (4) the inferred inner disk radius increased by a factor of ∼4. The change in the accretion disk inner radius during the outburst is in contrast to results from other soft X-ray transients. We find that the disk blackbody temperature depends on the inner disk radius roughly as T∝r^–3/4. For a standard Shakura-Sunyaev disk model this implies that the inferred mass accretion rate at the inner disk radius did not change appreciably during the part of the outburst observed by BeppoSAX.