Relations between X-ray timing features and spectral parameters of
  Galactic black hole X-ray binaries
  We present a study of correlations between spectral and timing parameters for
a sample of black hole X-ray binary candidates. Data are taken from GX 339-4, H
1743-322, and XTE J1650-500, as the Rossi X-ray Timing Explorer (RXTE) observed
complete outbursts of these sources. In our study we investigate outbursts that
happened before the end of 2009 to make use of the high-energy coverage of the
HEXTE detector and select observations that show a certain type of
quasi-periodic oscillations (type-C QPOs). The spectral parameters are derived
using the empirical convolution model simpl to model the Comptonized component
of the emission together with a disc blackbody for the emission of the
accretion disc. Additional spectral features, namely a reflection component, a
high-energy cut-off, and excess emission at 6.4 keV, are taken into account.
Our investigations confirm the known positive correlation between photon index
and centroid frequency of the QPOs and reveal an anticorrelation between the
fraction of up-scattered photons and the QPO frequency. We show that both
correlations behave as expected in the "sombrero" geometry. Furthermore, we
find that during outburst decay the correlation between photon index and QPO
frequency follow a general track, independent of individual outbursts.
