Studying accretion flows and probing strong gravitational fields using black hole X-ray binaries

The goal of this thesis is to use black hole X-ray binaries as a laboratory for studying the physics of accretion disks and to probe the strong gravitational fields around black holes where general relativity can be put to the test at its most extreme limits. X-ray spectral and timing observations of the black hole X-ray novae GRO J1655-40 and XTE J1550-564 provided by the Rossi X-ray Timing Explorer (RXTE) are the focus of this study. Both sources are observed in a succession of canonical outburst states of black hole X-ray novae. Apparent variations of the inner disk radius are probably caused by the failure of the multicolor disk/power-law model; the actual physical radius of the inner disk may remain fairly constant. The most likely value for the inner disk radius in GRO J1655-40 implies a dimensionless angular momentum for the black hole <0.7. The frequency and amplitude of 0.08--22 Hz Quasiperiodic X-ray Oscilations (QPOs) are well correlated with the X-ray spectral parameters, although the correlations found for XTE J1550-564 are generally opposite to those for GRO J1655-40. There is one exception: Both sources exhibit a general increase in the QPO frequency as the disk flux increases. In addition, these QPOs are observed only when the power-law component contributes more than 20% of the 2--20 keV flux, which indicates that both the disk and the power-law components are linked to the QPO phenomenon. In the case of XTE J1550-564, there are three fundamental types of QPO behavior which can be grouped according to the relative contributions of the disk and power-law components to the total flux.