GX 339-4: the distance, state transitions, hysteresis and spectral correlations

We study the X-ray variability and distance of GX 339-4. We derive the distance of greater than or similar to7 kpc, based on a recent determination of the binary parameters. We study data from the All-Sky Monitor (ASM) aboard Ginga, the Burst and Transient Source Experiment aboard the Compton Gamma Ray Observatory, and the ASM, Proportional Counter Array and High-Energy Transient X-ray Experiment aboard the Rossi X-ray Timing Explorer (RXTE). From 1987 to 2004, GX 339 4 underwent similar to15 outbursts and went through all known states of black hole binaries. For the first time, we present the PCA data from the initial hard state of the outburst of 2004. We then study colour-colour and colour-flux correlations. In the hard state, there is a strong anticorrelation between the 1.5-5 and 3-12 keV spectral slopes, which we explain by thermal Comptonization of disc photons. There is also a softening of the spectrum above 3 keV with the increasing flux that becomes stronger with increasing energy up to similar to200 keV. This indicates an anticorrelation between the electron temperature and luminosity, explained by hot accretion models. In addition, we see a variable broad-band slope with a pivot at similar to200 keV. In the soft state, there is a high-energy tail with varying amplitude beyond a strong and variable blackbody component. We confirm the presence of pronounced hysteresis, with the hard-to-soft state transitions occurring at much higher (and variable) luminosities than the soft-to-hard transitions. We fitted the RXTE/ASM data with a model consisting of an outer accretion disc and a hot inner flow. State transitions are associated then with variations in the disc truncation radius, which we fitted as similar to6GM/c(2) in the soft state and several times that in the hard state. The disappearance of the inner disc takes place at a lower accretion rate than its initial appearance owing to the dependence of the transitions on the source history. We provide further evidence against the X-ray emission in the hard state being non-thermal synchrotron, and explain the observed radio-X-ray correlation by the jet power being correlated with the accretion power.