The infrared/X-ray correlation of GX 339−4: probing hard X-ray emission in accreting black holes

• Published in: Monthly notices of the Royal Astronomical Society 2009-11, Vol.400 (1), p.123-133
• Main Authors: Coriat, M., Corbel, S., Buxton, M. M., Bailyn, C. D., Tomsick, J. A., Körding, E., Kalemci, E.
• Format: Article
• Language: English
• Subjects: accretion; accretion discs; accretion, accretion discs; Astronomy; Astrophysics; Black holes; Earth, ocean, space; Exact sciences and technology; Infrared imaging systems; infrared: stars; ISM: jets and outflows; radio continuum: stars; stars: individual: GX 339−4; X-rays; X-rays: binaries
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2009.15461.x

GX 339−4 has been one of the key sources for unravelling the accretion ejection coupling in accreting stellar mass black holes. After a long period of quiescence between 1999 and 2002, GX 339−4 underwent a series of four outbursts that have been intensively observed by many ground-based observatories [radio/infrared (IR)/optical] and satellites (X-rays). Here, we present results of these broad-band observational campaigns, focusing on the optical–IR (OIR)/X-ray flux correlations over the four outbursts. We found tight OIR/X-ray correlations over four decades with the presence of a break in the IR/X-ray correlation in the hard state. This correlation is the same for all four outbursts. This can be interpreted in a consistent way by considering a synchrotron self-Compton origin of the X-rays in which the break frequency varies between the optically thick and thin regime of the jet spectrum. We also highlight the similarities and differences between optical/X-ray and IR/X-ray correlations which suggest a jet origin of the near-IR emission in the hard state while the optical is more likely dominated by the blackbody emission of the accretion disc in both hard and soft state. However, we find a non-negligible contribution of 40 per cent of the jet emission in the V band during the hard state. We finally concentrate on a soft-to-hard state transition during the decay of the 2004 outburst by comparing the radio, IR, optical and hard X-rays light curves. It appears that unusual delays between the peak of emission in the different energy domains may provide some important constraints on jet formation scenario.