Astronomy and Astrophysics, volume 340, 431-436 (1998/12-2)
The 1998 outburst of the X-ray transient 4U 1630-47 observed with BeppoSAX.
OOSTERBROEK T., PARMAR A.N., KUULKERS E., BELLONI T., VAN DER KLIS M., FRONTERA F. and SANTANGELO A.
Abstract (from CDS):
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.