Novel spectral-timing methods for X-ray binary variability studies

This work explores the connection between the spectral properties of the X-ray emission produced by black hole X-ray binaries (BHXRBs) and the variability properties of these sources that are embedded in lightcurves. While BHXRBs are mostly studied using ‘static observables‘ such as the average energy spectrum, a variability timescale-resolved study (in terms of Fourier-frequencies) provides a much stronger and more reliable tool for understanding the intricate physics and geometrical properties of accretion flows around stellar-mass black holes. In the present Thesis, we first show how the geometrical properties of the accretion disc can be mapped by combining spectra and frequency-resolved time-lags. A time-scale-dependent reflection model is developed in terms of Fourier-frequencies and compared to observational hard-state data of GX 339–4 obtainedwithXMM-Newton. Secondly, we explore the variability properties of the accretion disc in SWIFT J1753.5–0127 using a combination of novel spectraltiming methods and the soft X-ray coverage of XMM-Newton. Finally, we show the development of a novel technique for fitting correlated signals in the Fourier domain as a function of energy and Fourier-frequency that can prove particularly useful with high signal-to-noise datasets fromfuture X-ray missions.