Abstract
Cataclysmic variable stars are in many ways similar to X-ray binaries. Both types of systems possess an accretion disk, which in most cases can reach the surface (or event horizon) of the central compact object. The main difference is that the embedded gravitational potential well in X-ray binaries is much deeper than those found in cataclysmic variables. As a result, X-ray binaries emit most of their radiation at X-ray wavelengths, as opposed to cataclysmic variables which emit mostly at optical/ultraviolet wavelengths. Both types of systems display aperiodic broad-band variability which can be associated to the accretion disk. Here, the properties of the observed X-ray variability in XRBs are compared to those observed at optical wavelengths in CVs. In most cases the variability properties of both types of systems are qualitatively similar once the relevant timescales associated with the inner accretion disk regions have been taken into account. The similarities include the observed power spectral density shapes, the rms-flux relation as well as Fourier-dependant time lags. Here a brief overview on these similarities is given, placing them in the context of the fluctuating accretion disk model which seeks to reproduce the observed variability.
Highlights
Cataclysmic variables (CVs) are close interacting binary systems where a late-type star transfers material to a white dwarf (WD) companion via Roche lobe overflow
X-ray binaries (XRBs) are compact interacting binaries which are similar to CVs in many ways, but where the accreting compact object is either a black hole (BH) or a neutron star (NS)
XRBs have shown variability ranging from milliseconds to hours, whilst for CVs this ranges from seconds to days
Summary
Cataclysmic variables (CVs) are close interacting binary systems where a late-type star transfers material to a white dwarf (WD) companion via Roche lobe overflow. X-ray binaries (XRBs) are compact interacting binaries which are similar to CVs in many ways, but where the accreting compact object is either a black hole (BH) or a neutron star (NS) Both CVs and XRBs, as well as active galactic nuclei (AGN; accreting supermassive BHs), have been shown to display strong aperiodic variability on a broad range of time-scales as well as in different wavelength ranges. CV timing studies have been facilitated thanks to the advent of the Kepler satellite (Gilliland et al 2010; Jenkins et al 2010), which is able to provide long, uninterrupted and high-precision light curves in the optical light from space Thanks to these capabilities it is possible to probe over four orders of magnitude in temporal frequency in CVs. More importantly, it is possible to compare the aperiodic variability properties observed in XRBs to those. Scaringi observed in CVs after taking into account the relevant 3 Fourier-Dependent Time-Lags in timescale and wavelength “translations”
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