SWIFT XRT Observations of the Nova-like Cataclysmic Variables MV Lyr, BZ Cam and V592 Cas

Abstract

We present a total of ~ 45 ksec (3$\times$15 ksec) of SWIFT XRT observations for three non-magnetic nova-like (NL) Cataclysmic Variables (CVs) (MV Lyr, BZ Cam, V592 Cas) in order to study characteristics of Boundary Layers (BL) in CVs. The nonmagnetic NLs are found mostly in a state of high mass accretion rate ($\ge$1$\times$10${}^{-9}$ Msun yr${}^{-1}$) and some show occasional low states. Using the XRT data, we find optically thin multiple-temperature cooling flow type emission spectra with X-ray temperatures (kT${}_{max}$) of 21-50 keV. These hard X-ray emitting boundary layers diverge from simple isobaric cooling flows indicating X-ray temperatures that are of virial values in the disk. In addition, we detect power law emission components from MV Lyr and BZ Cam and plausibly from V592 Cas which may be a result of the Compton scattering of the optically thin emission from the fast wind outflows in these systems and/or Compton up-scattering of the soft disk photons. The X-ray luminosities of the (multi-temperature) thermal plasma emission in the 0.1-50.0 keV range are (0.9-5.0)$\times$10${}^{32}$ erg/sec. The ratio of the X-ray and disk luminosities (calculated from the UV-optical wavelengths) yield an efficiency (L${}_x$/L${}_{disk}$) ~ 0.01-0.001. Given this non-radiative ratio for the X-ray emitting boundary layers with no significant optically thick blackbody emission in the soft X-rays (consistent with ROSAT observations) together with the high/virial X-ray temperatures, we suggest that high state NL systems may have optically thin BLs merged with ADAF-like flows and/or X-ray coronae. In addition, we note that the axisymmetric bipolar and/or rotation dominated fast wind outflows detected in these three NLs (particularly BZ Cam and V592 Cas) or some other NL may also be explained in the context of ADAF-like BL regions.

36 pages, 3 tables, 4 figures; Astrophysical Journal in PRESS

References in corpus (8)

• Modelling the behaviour of accretion flows in X-ray binaries
• Advection-Dominated Accretion and the Black Hole Event Horizon
• SW Sextantis stars: the dominant population of CVs with orbital periods between 3-4 hours
• ADAFs, accretion discs and outbursts in compact binaries
• Chandra HETG line spectroscopy of the Non-magnetic Cataclysmic Variable SS Cyg
• Modeling UX Ursae Majoris: An abundance of challenges
• Observations of V592 Cas - An Outflow at Optical Wavelengths
• X-ray Spectral Variations of U Gem from Quiescence to Outburst

Cited by in corpus (10)

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• ASAS J071404+7004.3 -- a close, bright nova-like cataclysmic variable with gusty winds
• Pre-outburst $Chandra$ Observations of the Recurrent Nova T Pyxidis
• X-ray properties of dwarf nova EY Cyg and the companion star using an XMM-Newton observation
• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• Line Driven Winds from Variable Accretion Discs
• XMM-Newton observation of V1504 Cyg as a probe for the existence of an evaporated corona
• X-ray emission mechanisms in accreting white dwarfs
• TUVO-21acq: a new cataclysmic variable discovered through a UV outburst