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

We study X-ray and variability and distance of GX 339-4. We derive d>7 kpc, based on recent determination of the binary parameters. We study data from the Ginga/ASM, the CGRO/BATSE, and the RXTE/ASM, PCA and HEXTE. From 1987 to 2004, GX 339-4 underwent 15 outbursts and went through all known states of black-hole binaries. We also present the PCA data from the initial stage of the 2004 outburst. 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 200 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 200 keV. 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 fit the 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 fit as 6GM/c^2 in the soft state and several times that in the hard state. The disappearence of the inner disc takes place at a lower accretion rate than its initial appearance due to the dependence of the transitions on the source history. We provide further evidence against the X-ray emission in the hard state being nonthermal synchrotron, and explain the observed radio-X-ray correlation by the jet power being correlated with the accretion power.Comment: MNRAS, in press (a substantially revised version, including new data from the Feb. 2004 outburst of GX 339-4

GRS 1915+105: the brightest Galactic black hole

We compare the evolution of spectral shape with luminosity in GRS 1915+105 with that of 'normal' black holes. The pathological time variability of GRS 1915+105 does not indicate that it belongs in a different class to all the other objects. At comparable fraction of Eddington luminosity its spectra and (more importantly) time variability behaviour are similar to that seen in the 'normal' black holes. Its unique limit-cycle variability only appears when it radiates at uniquely high (super-Eddington) luminosities.Comment: Accepted for publication in MNRA

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

We study X-ray and soft γ-ray variability of GX 339–4 from 1987 to 2003, as well as its distance, necessary for interpretation of our results. We derive it to be ∼ 8 kpc, based on recent determination of the orbital parameters. We then use data from the All-Sky Monitors aboard Ginga and RXTE, the BATSE detector aboard CGRO, and the PCA and HEXTE aboard RXTE. During this period, GX 339–4 underwent ∼15 outbursts and went through all the canonical states of black-hole binaries. We study colour-colour and colour-flux correlations during various states. In the hard state, there is a strong anticorrelation between the 1.5–5 and 3–12 keV spectral slopes, which we explain in the framework of thermal Comptonization of disc blackbody photons. There is also a softening of the spectrum above 3 keV with the increasing flux that becomes progressively more pronounced with energy up to 160 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 ∼200 keV. In the soft state, there is a high energy tail with varying amplitude beyond a stron