Modeling of High-Frequency Variability in X-ray Binaries with Black Holes

TL;DR

This paper models the aperiodic X-ray variability in black hole binaries, revealing how disk structure and relativistic effects shape the observed power spectra across different frequencies.

Contribution

It introduces a detailed model of the power spectra considering disk fluctuations and relativistic effects, explaining high-frequency variability suppression and additional features.

Findings

Power spectrum follows a power law with slope ~-1 at low frequencies.

High-frequency variability is suppressed by photon arrival time delays.

Relativistic effects cause additional variability around 200 Hz.

Abstract

The properties of the aperiodic variability in X-ray binaries with black holes are considered. The power spectra of the luminosity variability for a flat accretion disk that is an emission source with a power-law energy spectrum have been modeled. At low frequencies the derived power spectrum has the form of a power law with a slope $\rho\approx-1$ and a cutoff at a frequency approximately equal to the fluctuations characteristic frequency at the disk inner edge; at higher frequencies the power spectrum has a complex form. The high-frequency variability is suppressed due to the arrival time delays of the photons emerging in the different parts of the disk. The presence of azimuthal accretion rate fluctuations in the disk and the azimuthal non-uniformity of the disk surface brightness in the observer's imaginary plane caused by the relativistic effects give rise to an additional variability at frequencies $\sim$200 Hz.