Coronal-temporal correlations in GX 339-4: hysteresis, possible reflection changes and implications for advection-dominated accretion flows

We present spectral fits and timing analysis of Rossi X-ray Timing Explorer observations of GX 339-4. These observations were carried out over a span of more than two years and encompassed both the soft/high and hard/low states. Two observations were simultaneous with Advanced Satellite for Cosmology and Astrophysics observations. Hysteresis in the soft-hard state transition is observed. The hard state exhibits a possible anticorrelation between coronal compactness (i.e. spectral hardness) and the covering fraction of cold, reflecting material. The correlation between 'reflection fraction' and soft X-ray flux, however, appears to be more universal. Furthermore, low-flux, hard-state observations - taken over a decline into quiescence - show that the Fe line, independent of 'reflection fraction', remains broad and at a roughly constant equivalent width, counter to expectations from advection-dominated accretion flow models. All power spectral densities of the hard-state X-ray light curves are describable as the sum of just a few broad, quasi-periodic features with frequencies that roughly scale as coronal compactness, l(c) , to the -3/2 power. This is interpretable in a simple, toy model of an efficient spherical corona as variations of l(c) proportional toR (t) , where R (t) is the 'transition radius' between the corona and an outer thin disc. Similar to observations of Cyg X-1, time lags between soft and hard variability anticorrelate with coronal compactness, and peak shortly after the transition from the soft to the hard state. A stronger correlation is seen between the time lags and the 'reflection fraction'. These latter facts might suggest that the time lags are associated with the known, spatially very extended, synchrotron-emitting outflow.