Observational Signatures of Black Holes: Spectral and Temporal Features of XTE J1550−564

The theoretical predictions of the converging inflow, or bulk motion Comptonization (BMC) model are discussed and some predictions are compared to X-ray and gamma-ray observations of the high/soft state of Galactic black hole candidate XTE J1550-564. The ~10^2 Hz quasi-periodic oscillation phenomenon tends to be detected in the high state at times when the bolometric luminosity surges and the hard power-law spectral component is dominant. Furthermore, the power in these features increases with energy. We offer interpretation of this phenomenon as oscillations of the innermost part of the accretion disk, which in turn supplies the seed photons for the converging inflow where the hard power law is formed through BMC. We further argue that the noted lack of coherence between intensity variations of the high/soft state low- and high-energy bands is a natural consequence of our model and that a natural explanation for the observed hard and soft lag phenomenon is offered. In addition, we address some criticisms of the BMC model supporting our claims with observational results. For XTE J1550-564, assuming the source is 5 kpc distant, we derive a black hole mass estimate of 12-15 solar masses through application of the BMC model