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X-ray variability of accreting black hole binaries is believed to be producedby the fluctuations propagating towards the compact object. Observationssuggest the light curves in different energy bands are connected, but thefluctuations at harder energies are delayed with respect to the softer ones.The standard interpretation involves dependence of the X-ray spectral hardnesson the radial distance, with harder spectra emitted closer to the black hole.Recently, a number of challenges to this scenario have been found, both atqualitative and quantitative level. The model does not predict the largemagnitude of the delay between different energies, as well as the dependence ofvariability amplitude on the spectral range and frequency. We study timingproperties of accreting black hole X-ray binaries taking into accountpeculiarities of spectral formation in these sources. We show that thesimultaneous presence of two components leads to a complex shape of powerspectra and phase lags between the X-ray bands: the amplitude of the phase lagbecomes independent of the delay between the components, and the power spectrashow an artificial decrease or, on the contrary, enhancement of power at lowFourier frequencies. This provides an essential ingredient for thereinstatement of the propagating fluctuations model. The work draws attentionto the importance of considering conditions of spectral formation when studyingtiming properties.

Interplay of spectral components in timing properties of accreting compact objects