Accretion Flow in the inner Accretion Discs of Cataclysmic Variables
Abstract
We study nature of time variability of brightness of non-magnetic cataclysmic variables. We show that lightcurtves of all analyzed DN systems in UV and X-ray energy bands demonstrate band limited noise, which can be adequately described in the framework of the model of propagating fluctuations. The frequency of the break indicates the inner disc truncation with a range of radii (10-3)e+9 cm. We analyse the RXTE and optical (RTT150) data of SS Cyg in outburst and quiescence which show that during the outburst the inner disk radius moves towards the white dwarf and receeds as the outburst declines to quiescence. Cross-correlations between the simultaneous UV and X-ray light curves find time lags in the X-rays of 90-180 sec consistent with travel time of matter from a truncated inner disc to the white dwarf surface. This suggests that DN and other plausible nonmagnetic systems have truncated accretion discs indicating that the accretion may occur through coronal flows in the disc. We compare and contrast magnetic and nonmagnetic systems in terms of their aperiodic noise characteristics and the model of propagating fluctuations. The comparison of the X-ray/UV time lag observed by us in the case of non-magnetic CVs with those, detected for magnetic CVs allows us to make an rough estimate of the viscosity parameter. Multi band simultaneous observations of coming observattories like ASTROSAT will give us the opportunity to study time variability of brightness variations of accretion disks in cataclysmic variables in quiescence and outburst using LAXPC and UVIT/OPT instruments. We will elaborate on the nature and possible outcomes of such research.
- Publication:
-
39th COSPAR Scientific Assembly
- Pub Date:
- July 2012
- Bibcode:
- 2012cosp...39...92B