A Unified Description of the Timing Features of Accreting X‐Ray Binaries

TLDR

The study proposes an empirical model that unifies the power spectra of accreting neutron stars and black holes, enabling consistent comparison of high‑ and low‑coherence timing features across diverse source types and states. The model represents power spectra as a superposition of multiple Lorentzians, applied to six accreting X‑ray binaries, thereby treating all QPO and noise components uniformly without pre‑classifying them. The model accurately fits the observed spectra without requiring a scale‑free 1/f component, and it refines frequency correlations, revealing similarities that suggest common underlying physics across different systems.

Abstract

We study an empirical model for a unified description of the power spectra of accreting neutron stars and black holes. This description is based on a superposition of multiple Lorentzians and offers the advantage that all QPO and noise components are dealt with in the same way, without the need of deciding in advance the nature of each component. This approach also allows us to compare frequencies of features with high and low coherences in a consistent manner and greatly facilitates comparison of power spectra across a wide range of source types and states. We apply the model to six sources, the low-luminosity X-ray bursters 1E 1724-3045, SLX 1735-269 and GS 1826-24, the high-latitude transient XTE J1118+480, the bright system Cir X-1, and the Z source GX 17+2. We find that it provides a good description of the observed spectra, without the need for a scale-free (1/f) component. We update previously reported correlations between characteristic frequencies of timing features in the light of this new approach and discuss similarities between different types of systems which may point towards similar underlying physics.