X-ray Spectra and Light Curves of Cooling Novae and a Nova-Like

Abstract

We present X-ray observations of novae V2491 Cyg and KT Eri about 9 years post-outburst, of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM-Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times 10^{-9}-10^{-8}{M}_{\odot }/yr$, while for KT Eri, $\dot{m}<2\times 10^{-10}{M}_{\odot }/yr$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of ~39 minutes, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim 1.8\times 10^{-11}{M}_{\odot }/yr$, one magnitude lower than KT Eri, consistently with its U Gem outburst behavior and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system's low inclination, probably due to the X-ray flux of the secondary. A period of ~81 minutes is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

14 pages, 12 figures, 6 tables

References in corpus (8)

• Magnetic White Dwarfs
• The Morphology of the Expanding Ejecta of V2491 Cygni (2008 N.2)
• Short-period X-ray oscillations in super-soft novae and persistent SSS
• X-ray observations of VY Scl type nova-like binaries in the high and low state
• Theoretical Studies of Accretion of Matter onto White Dwarfs and the Single Degenerate Scenario for Supernovae of Type Ia
• Pre-nova X-ray observations of V2491 Cyg (Nova Cyg 2008b)
• Determination of the basic parameters of the dwarf nova EY Cygni
• X-ray properties of dwarf nova EY Cyg and the companion star using an XMM-Newton observation

Cited by in corpus (4)

• The multi-wavelength view of shocks in the fastest nova V1674 Her
• The Nova KT Eri Is a Recurrent Nova With a Recurrence Time-Scale of 40-50 Years
• Chandra observations of nova KT Eridani in outburst
• A light curve model of V2491 Cyg: Classical nova outburst on a cool and massive white dwarf