Disk structure of cataclysmic variables and broadband noise characteristics in comparison with XRBs

Abstract

Flicker noise and its variations in accreting systems have been a diagnostic tool in understanding accretion disk structure and state transitions. I present broadband noise variations of nonmagnetic cataclysmic variables (CVs) in comparison with magnetic CVs (MCV) extrapolating the comparisons into X-ray binaries (XRB), mostly in the X-ray wavelengths. CVs demonstrate band-limited noise in the UV and X-ray energy bands (and also optical), which can be adequately explained in the framework of the model of propagating fluctuations). The detected frequency breaks in the nonmagnetic CVs are in the range 1-6 mHz in quiescence and indicate an optically thick disk truncation (i.e., transition) showing the existence of advective (ADAF-like) hot flows in the inner regions. Analysis of other available data (e.g., SS Cyg, SU UMa, WZ Sge, and Z Cha) reveals that during the outburst the inner disk radius moves toward the white dwarf and recedes as the outburst declines (with some exceptions) while changes in the X-ray energy spectrum are also observed. Cross-correlations between the simultaneous optical, UV, and X-ray light curves show time lags consistent with truncated optically thick disk-like and ADAF-like hot flows in the inner disk. I also discuss the hysteresis effect in dwarf novae and show that the X-ray temperatures and break frequencies anticorrelate indicating the energy exchange in the disk flow as the accretion state of the source changes.