| We present calculations of non-LTE, relativistic, thin accretion disk models applicable to the thermal state of black hole X-ray binaries. We include the effects of thermal Comptonization and bound-free and free-free opacities of all abundant ion species. Taking into account the relativistic propagation of photons from the local disk surface to an observer at infinity, we present spectra calculated for a variety of accretion rates, black hole spins, inclinations, and stress prescriptions. We explore the effects of varying the dissipation profile and including magnetic pressure support on the vertical structure and spectra of the disk. We find that the effective photosphere usually lies at a small fraction of the total column depth, producing spectra that are remarkably independent of the stress prescription and vertical structure assumptions. However, a significant hardening of the spectrum can occur if magnetic pressure support is considered, a torque on the inner edge of the disk is included, a sufficiently large fraction of the dissipations occurs above the effective photosphere, or the disk annuli become effectively optically thin.; We have used these methods to construct a spectral fitting model (BHSPEC) for direct comparison with observations. We argue that existing data warrant spectral modeling which both accounts for relativistic effects, and treats the physics of radiative transfer in detail. We present results from spectral modeling of three black hole X-ray binaries: LMC X-3, GRO J1655-40, and XTE J1550-564. We fit the data with a range of spectral models that includes a multitemperature blackbody, a relativistic accretion disk with color-corrected blackbodies, and BHSPEC. We find that BHSPEC provides the best fit for a BeppoSAX observation of LMC X-3, which has the broadest energy coverage of our sample. It also provides the best fit for multiple epochs of RXTE data in this source, except at the highest luminosities ( L/LEdd ≳ 0.7). BHSPEC is also the best-fit model for multi-epoch observations of GRO J1655-40 and XTE J1550-564, although the best-fit inclination of the inner disk differs from the binary inclination. In all three sources our fits imply moderate black hole spins (a* ∼ 0.1-0.8). |
