Black hole binaries quasi-periodic oscillations

We have considered all the black hole binaries that have been densely monitored by the Rossi X-ray Timing Explorer satellite. We find that the amplitude of low-frequency quasi-periodic oscillations (QPOs) depends on the orbital inclination.

Type-C QPOs are stronger for nearly edge-on systems (high inclination), while type-B QPOs are stronger when the accretion disc is closer to face-on (low inclination). Our results also suggest that the noise associated with type-C QPOs is consistent with being stronger for low-inclination sources, while the noise associated with type-B QPOs seems inclination independent. These results are consistent with a geometric origin of the type-C QPOs - for instance arising from relativistic precession of the inner flow within a truncated disc - while the noise would correspond to intrinsic brightness variability from mass accretion rate fluctuations in the accretion flow.