Complex lags from simple physics

Astronomy and Astrophysics, vol. 714, pp. A329

Abstract

Context. X-ray timing information obtained through Fourier analysis of the variable emission from black hole X-ray binaries has been used for several decades to provide key insights into the physical properties of these systems that are not measurable with spectroscopy. In particular, quasi-periodic oscillations (QPOs) within these systems have been of particular interest and remain the subject of considerable debate regarding their origin. Aims. We investigated the timing products of simple toy models of QPO variability to provide greater insight into the interpretation of signals produced by these sources. Methods. We simulated simple physical setups and show how phase lags and coherence of the signals change between these setups. We first focused on the properties of QPO-like signals under a single-driving-signal assumption. We then investigated the case of multiple oscillations in a signal. Finally, we investigated how timing products change when QPOs are produced by time-dependent modulation of periodic signals. Results. Many simple physical setups with common driving signals can reproduce complex non-linear phase lags that resemble those present in the data. Changes in the physical setup align with features in the data, such as differing power spectra, but do not reproduce the data as expected. Multiple incoherent processes present in the signal struggle to reproduce the behaviour observed in the data. Coherence appears to be a more useful tool for distinguishing between setups. Conclusions. Fourier analysis of complex data, such as those produced by X-ray binaries, can lead to the invocation of exotic lag mechanisms without the appropriate framing. This paper provides tools for understanding how different phenomena in signals, particularly those relating to QPOs, can result in non-linear phase lags with explicit structure.

Authors 2

1. Benjamin Ricketts Aachen

   University of Amsterdam · Space Research Organisation Netherlands

   Affiliation as printed

   Anton Pannekoek Institute, University of Amsterdam

   SRON

2. G. Marcel
   Affiliation as printed

   Department of Physics and Astronomy