Integral and XMM-Newton spectroscopy of GX 339-4 during hard/soft intermediate and high/soft states in the 2007 outburst

Abstract

We present simultaneous XMM-Newton and International Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the luminous black hole transient and relativistic jet source GX 339-4. GX 339-4 started an outburst on 2006 November and our observations were undertaken from 2007 January to March. We triggered five INTEGRAL and three XMM-Newton Target of Opportunity observations within this period. Our data cover different spectral states, namely hard intermediate, soft intermediate, and high/soft. We performed spectral analysis to the data with both phenomenological and more physical models and found that a nonthermal component seems to be required by the data in all the observations. We find a hardening of the spectrum in the third observation coincident with appearance of a broad and skewed Fe Kα line. In all spectral states joint XMM/EPIC-pn, JEM-X, ISGRI, and SPI data were fitted with the hybrid thermal/nonthermal Comptonization EQPAIR model. While this model accounts very well for the high-energy emission observed, it has several drawbacks in the description of the lower-energy channels. Our results imply evolution in the coronal properties, the most important one being the transition from a compact corona in the first observation to the disappearance of coronal material in the second and reappearance in the third. This fact, accompained by the plasma ejection events detected in radio on February 4-18, suggest that the ejected medium is the coronal material responsible for the hard X-ray emission. © 2009. The American Astronomical Society. All rights reserved.