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arXiv · 0810.3556

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. Mendez·M. van der Klis
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Abstract

We report on X-ray and soft gamma-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-intermediate state 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 the high-energy cut-off or in terms of a variations in the reflection component. We compare our results with those from a similar transition during the 2004 outburst of GX 339-4.

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M. Del Santo, T. M. Belloni, J. Homan, A. Bazzano, P. Casella, R. P. Fender, E. Gallo, N. Gehrels, W. H. G. Lewin, M. Mendez, M. van der Klis. 2008-10-20. Broad-band X-ray spectral evolution of GX 339-4 during a state transition. https://doi.org/10.1111/j.1365-2966.2008.14111.x

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