Evidence of Light-Bending Effects and its implication for spectral state transitions. (arXiv:1208.3277v1 [astro-ph.HE])

Evidence of Light-Bending Effects and its implication for spectral state transitions. (arXiv:1208.3277v1 [astro-ph.HE]):
It has long been speculated that the nature of the hard X-ray corona may be
an important second driver of black hole state transitions, in addition to the
mass accretion rate through the disk. However, a clear physical picture of
coronal changes has not yet emerged. We present results from a systematic
analysis of Rossi X-ray Timing Explorer observations of the stellar mass black
hole binary XTE J1650-500. All spectra with significant hard X-ray detections
were fit using a self-consistent, relativistically-blurred disk reflection
model suited to high ionization regimes. Importantly, we find evidence that
both the spectral and timing properties of black hole states may be partially
driven by the height of the X-ray corona above the disk, and related changes in
how gravitational light bending affects the corona--disk interaction.
Specifically, the evolution of the power-law, thermal disk, and
relativistically--convolved reflection components in our spectral analysis
indicate that: (1) the disk inner radius remains constant at $r_{in}
=1.65\pm0.08 GM/c^2$ (consistent with values found for the ISCO of XTE
J1650-500 in other works) throughout the transition from the brighter phases of
the low-hard state to the intermediate states (both the hard-intermediate and
soft-intermediate), through to the soft state and back; (2) the ratio between
the observed reflected X-ray flux and power-law continuum (the "reflection
fraction", $R$) increases sharply at the transition between the
hard-intermediate and soft-intermediate states ("cannonball" jets are sometimes
launched at this transition); (3) both the frequency and coherence of the
high-frequency quasi-periodic oscillations (QPOs) observed in XTE J1650-500
increase with $R$. We discuss our results in terms of black hole states and the
nature of black hole accretion flows across the mass scale.