Short term aperiodic variability of X-ray binaries: its origin and implications

TL;DR

This review discusses recent progress in understanding the aperiodic variability of accreting X-ray binaries, emphasizing models that explain observational features and insights into neutron star properties.

Contribution

It summarizes current models of X-ray variability and demonstrates how variability analysis helps determine neutron star masses and radii.

Findings

Resolved the contribution of accretion disk and boundary layer to X-ray spectra.

Estimated neutron star masses and radii from spectral variability.

Validated models explaining the variability of accreting sources.

Abstract

In this review I briefly describe the latest advances in studies of aperiodic variability of accreting X-ray binaries and outline the model which currently describe the majority of observational appearances of variability of accreting sources in the best way. Then I concentrate on the case of luminous accreting neutron star binaries (in the soft/high spectral state), where study of variability of X-ray emission of sources allowed us to resolve long standing problem of disentangling the contribution of accretion disk and boundary/spreading layer components to the time average spectrum of sources. The obtained knowledge of the shape of the spectrum of the boundary layer allowed us to make estimates of the mass and radii of accreting neutron stars.