Journal Article

Broad-band X-ray spectral evolution of GX 339−4 during a state transition*

M. Del Santo, T. M. Belloni, J. Homan, A. Bazzano, P. Casella, R. P. Fender, E. Gallo, N. Gehrels, W. H. G. Lewin, M. Méndez and M. Van Der Klis

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 392, issue 3, pages 992-997
Published in print January 2009 | ISSN: 0035-8711
Published online January 2009 | e-ISSN: 1365-2966 | DOI:
Broad-band X-ray spectral evolution of GX 339−4 during a state transition*

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We report on X-ray and soft γ-ray observations of the black hole candidate GX 339−4 during its 2007 outburst, performed with the RXTE and INTEGRAL satellites. The hardness–intensity diagram of all RXTE/PCA data combined shows a q-shaped track similar to that observed in previous outbursts. The evolution in the diagram suggested that a transition from hard- to soft-intermediate state occurred, simultaneously with INTEGRAL observations performed in March. The transition is confirmed by the timing analysis presented in this work, which reveals that a weak type-A quasi-periodic oscillation (QPO) replaces a strong type-C QPO. At the same time, spectral analysis shows that the flux of the high-energy component shows a significant decrease in its flux. However, we observe a delay (roughly one day) between variations of the spectral parameters of the high-energy component and changes in the flux and timing properties. The changes in the high-energy component can be explained either in terms of the high-energy cut-off or in terms of variations in the reflection component. We compare our results with those from a similar transition during the 2004 outburst of GX 339−4.

Keywords: accretion, accretion discs; black hole physics; stars: individual: GX 339−4; X-ray: binaries

Journal Article.  4271 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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