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Astron. Astrophys. 340, 431-436 (1998)

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The 1998 outburst of the X-ray transient 4U 1630-47 observed with BeppoSAX

T. Oosterbroek 1, A.N. Parmar 1, E. Kuulkers 2, T. Belloni 3, M. van der Klis 3, F. Frontera 4 and A. Santangelo 5

1 Astrophysics Division, Space Science Department of ESA, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands
2 Astrophysics, University of Oxford, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK
3 Astronomical Institute, University of Amsterdam and Center for High-Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
4 Istituto TESRE, CNR, via Gobetti 101, I-40129 Bologna, Italy
5 IFCAI, CNR, via La Malfa 153, I-90146 Palermo, Italy

Received 10 August 1998 / Accepted 30 September 1998

Abstract

We report results of five pointed BeppoSAX observations of the black hole candidate 4U 1630-47 during part of its 1998 outburst when the 2-10 keV source luminosity decreased from [FORMULA] erg s-1 (for an assumed distance of 10 kpc) by a factor of [FORMULA]7. The 2-200 keV 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 [FORMULA]20 keV 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 [FORMULA]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 [FORMULA]. 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 .

Key words: X-rays: stars – stars: individual: 4U 1630-47

Send offprint requests to: T. Oosterbroek (toosterb@astro.estec.esa.nl)

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© European Southern Observatory (ESO) 1998

Online publication: November 9, 1998
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