Geometrical constraints on the origin of timing signals from black holes

TL;DR

This study investigates how the orbital inclination of black-hole binaries influences their fast variability signals, revealing geometric dependencies of different QPO types and supporting models involving relativistic precession and jet activity.

Contribution

It provides the first systematic analysis of inclination effects on black-hole transient variability, linking QPO types to geometric and jet-related phenomena.

Findings

Type-C QPOs are stronger in high-inclination systems.

Type-B QPOs are stronger in low-inclination systems.

Type-C QPO noise is more prominent in low-inclination sources.

Abstract

We present a systematic study of the orbital inclination effects on black-hole transients fast time-variability properties. We have considered all the black-hole binaries that have been densely monitored by the Rossi XTE 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 disk 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 to 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 disk - while the noise would correspond to intrinsic brightness variability from mass accretion rate fluctuations in the accretion flow. The opposite behavior of type-B QPOs - stronger in low inclinations sources - supports the hypothesis that type-B QPOs are related to the jet, the power of which is the most obvious measurable parameter expected to be stronger in nearly face-on sources.