A Global Spectral Study of Black Hole X-ray Binaries
  (Abridged) We report on a consistent and comprehensive spectral analysis of
the X-ray emission of 25 Black Hole X-ray Binaries. All publicly available
observations of the black hole binaries in the RXTE archive were analysed.
Three different types of model were fitted to investigate the spectral changes
occurring during an outburst. For the population, as well as each binary and
each outburst from each binary, we construct two diagnostic diagrams. The
Hardness Intensity/Luminosity Diagram (HID/HLD) is most useful when studying a
single binary. However, to compare between different binary systems, the Disc
Fraction Luminosity diagram (DFLD) is more useful. We discuss the limitations
of both diagnostic diagrams for the study of the X-ray binary outbursts, and we
clearly illustrate how the two diagrams map onto each other for real outburst
data. We extract the peak luminosities in a single outburst, as well as the
luminosities at the transitions away from- and returning to the powerlaw
dominated state for each outburst. The distribution of the luminosities at the
transition from the powerlaw to the disc dominated state peaks at around
0.3L_Edd, the same as the peak of the distribution of the peak luminosities in
an outburst. Using the disc fraction to calculate the transition luminosities
shows that the distributions of the luminosities for the transitions away from-
and return to the powerlaw dominated state are both broad and appear to
overlap. Finally we compare the measured X-ray luminosities with a small number
of contemporaneous radio measurements. Overall this is the most comprehensive
and uniform global study of black hole X-ray binaries to date.
