Overview of an Extensive Multi-wavelength Study of GX 339-4 during the 2010 Outburst

The microquasar GX 339-4 experienced a new outburst in 2010: it was observedsimultaneously at various wavelengths from radio up to soft gamma-rays. Wefocused on observations that are quasi-simultaneous with those made with theINTEGRAL and RXTE satellites: these were collected in 2010 March-April duringour INTEGRAL Target of Opportunity program, and during some of the otherINTEGRAL observing programs with GX 339-4 in the field-of-view. X-raytransients are extreme systems that often harbour a black hole, and are knownto emit throughout the whole electromagnetic spectrum when in outburst. Thegoals of our program are to understand the evolution of the physical processesclose to the black hole and to study the connections between the accretion andejection. We analysed radio, NIR, optical, UV, X-ray and soft gamma-rayobservations. We studied the source evolution in detail by producing lightcurves, hardness-intensity diagrams and spectra. We fitted the broadband datawith phenomenological, then physical, models to study the emission coming fromthe distinct components. Based on the energy spectra, the source evolved fromthe canonical hard state to the canonical soft state. The source showed X-rayspectral variations that were correlated with changes in radio, NIR and opticalemission. The bolometric flux increased from 0.8 to 2.9*10^{-8} erg cm^{-2}s^{-1} while the relative flux and contribution of the hot medium globallydecreased. Reprocessing in the disc was likely to be strong at the end of ourobservations. The source showed a behaviour similar to that of previousoutbursts, with some small deviations in the hard X-rays parameters' evolution.The radio, NIR and optical emission from jets was detected, and seen to fade asthe source softened. The results are discussed within the context of disc andjet models.