Spectral-Timing studies of high state Cataclysmic Variables
Abstract
Analysis of aperiodic variability and broadband noise have been used as a diagnosis technique for understanding disk structure and state transitions in accreting binaries. Long time-scale variability in CV disks may be created in the outer parts of the accretion disk, but the relatively short-time variability (at f ≥ few mHz) originates in the inner parts (Balman & Revnivtsev 2012, Balman 2019, 2020). Properties of this noise are similar to that of the X-ray binaries with neutron stars and black holes and is explained with the model of propagating fluctuations. CVs demonstrate band limited noise (BLN) in the UV, X-ray and optical, with detected frequency breaks in the nonmagnetic CVs (mainly DNe) in the range (1-6) mHz in quiescence and indicate an optically thick disk truncation (transition) showing existence of advective hot flows (RIAF ADAF-like flows) in the inner regions. Cross-correlations between the simultaneous optical, UV and X-ray light curves show time lags (propagation lags about 1.5-3 min), yet again consistent with truncated optically thick disk. Here, I focus on the high state CVs and their broadband noise characteristics (mainly X-ray) in relation to their X-ray spectra and the accretion rate of the systems (10-9 - few × 10-8 M_{⊙}/yr) with their outflow characteristics. I find similar broadband noise to DNe with BLN noise breaking in a range 2.5-10 mHz and prominent Lorentzian noise components dominating the BLN with occasional mHz QPOs (e.g., 2 mHz) as the accretion rate increases with spectral characteristics revealing nonequilibrium ionization plasma (Balman et al. 2021). There is also a power law component that becomes more prominent with increasing accretion rate. I will give examples using NuSTAR and XMM-Newton data inconjunction with other observatories. Also I discuss, multiwavelength time-lag properties which I find, at times, revealing hard or soft lags in the X-rays (∼5-20 s). I elaborate spectral-timing characteristics in the light of radiatively inefficient advective hotflows in CVs.
- Publication:
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44th COSPAR Scientific Assembly. Held 16-24 July
- Pub Date:
- July 2022
- Bibcode:
- 2022cosp...44.2367B