X-ray and UV observations of V751 Cyg in an optical high state

Abstract

Aims: The VY Scl system (anti-dwarf nova) V751 Cyg is examined following a claim of a super-soft spectrum in the optical low state. Methods: A serendipitous XMM-Newton X-ray observation and, 21 months later, Swift X-ray and UV observations, have provided the best such data on this source so far. These optical high-state datasets are used to study the flux and spectral variability of V751 Cyg. Results: Both the XMM-Newton and Swift data show evidence for modulation of the X-rays for the first time at the known 3.467 hr orbital period of V751 Cyg. In two Swift observations, taken ten days apart, the mean X-ray flux remained unchanged, while the UV source brightened by half a magnitude. The X-ray spectrum was not super-soft during the optical high state, but rather due to multi-temperature optically thin emission, with significant (10^{21-22} cm^-2) absorption, which was higher in the observation by Swift than that of XMM-Newton. The X-ray flux is harder at orbital minimum, suggesting that the modulation is related to absorption, perhaps linked to the azimuthally asymmetric wind absorption seen previously in H-alpha.

arXiv comment6 pages, 9 figures, accepted for publication in A&A

References in corpus (16)

• On the Absorption of X-rays in the Interstellar Medium
• The Swift X-ray Telescope
• The European Photon Imaging Camera on XMM-Newton: The MOS Cameras
• Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
• The Swift Ultra-Violet/Optical Telescope
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• Photometric Calibration of the Swift Ultraviolet/Optical Telescope
• Catalogue of cataclysmic binaries, low-mass X-ray binaries and related objects (Seventh edition)
• A Bayesian test for periodic signals in red noise
• A Self-Occulting Accretion Disk in the SW Sex Star DW UMa
• The 7.1 hour X-ray-UV-NIR period of the gamma-ray classical Nova Monocerotis 2012
• X-ray observations of VY Scl type nova-like binaries in the high and low state
• ASCA X-ray observations of the disk wind in the dwarf nova Z Camelopardalis
• The X-ray Spectra of VY Scl Stars Are Not Blackbodies
• Hubble Space Telescope STIS Spectroscopy of Three Peculiar Nova-Like Variables: BK Lyn, V751 Cygni and V380 Oph
• Far Ultraviolet Spectral Analysis of the Prototype Nova-Like Variable VY Sculptoris from the High State to the Low State

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• Broad Observational Perspectives Achieved by the Accreting White Dwarf Sciences in the XMM-Newton and Chandra Eras
• MACHO 311.37557.169: A VY Scl star