Geometrical Effect of Supercritical Accretion Flows: Observational Implications of Galactic Black-Hole Candidates and Ultraluminous X-ray Sources

We investigate the dependence of the viewing angle in supercritical accretion flows and discuss the observational implications of galactic black-hole candidates and ultraluminous X-ray sources. When the mass accretion rate exceeds the critical rate, then the shape of the disk is geometrically thick due to the enhanced radiation pressure. The model spectra of supercritical accretion flows strongly depend on the inclination angle. Because the outer disk blocks the emission from the disk inner region for high inclination angle. We also find that the spectral properties of low-inclination angle and low accretion-rate disks are very similar to those of high-inclination and high accretion rate disks. That is, if an object has a high inclination and high accretion rate, such a system suffers from self-occultation and the spectrum will be extremely soft. Therefore, we cannot discriminate these differences from spectrum shapes only. Conversely, if we use the self-occultation properties, we could constrain the inclination angle of the system. We suggest that some observed high temperature ultraluminous X-ray sources have near face-on geometry, i < 40, and Galactic black hole candidate, XTE J1550-564, possesses relatively high-inclination angles, i > 60.

K. Watarai, K. Ohsuga, R. Takahashi, J. Fukue · 2005