INTEGRAL/RXTE high-energy observation of a state transition of GX 339-4
Belloni, T.; Miller, J. M.; Homan, J.; van der Klis, M.; Lewin, W. H. G.; Casella, P.; Fender, R. P.; Del Santo, M.; Méndez, M.; Parolin, I.
Italy, United States, United Kingdom, Netherlands
Abstract
On 2004 August 15, we observed a fast (shorter than 10 h) state transition in the bright black hole transient GX 339-4 simultaneously with Rossi X-Ray Timing Explorer (RXTE) and INTEGRAL. This transition was evident both in timing and spectral properties. Combining the data from the Proportional Counter Array (PCA), the High-Energy X-ray Timing Experiment (HEXTE) and the Imager on Board the INTEGRAL Satellite (IBIS), we obtained good quality broad-band (3-200 keV) energy spectra before and after the transition. These spectra indicate that the hard component steepened. Also, the high-energy cut-off that was present at ~70 keV before the transition was not detected after the transition. This is the first time that an accurate determination of the broad-band spectrum across such a transition has been measured on a short time-scale. It shows that, although some spectral parameters do not change abruptly through the transition, the high-energy cut-off increases/disappears rather fast. These results constitute a benchmark on which to test theoretical models for the production of the hard component in these systems.