Chandra Observation of V426 Oph: Weighing the Evidence for a Magnetic White Dwarf

Abstract

We report the results of a 45 ks Chandra observation of the cataclysmic variable V426 Ophiuchus. The high resolution spectrum from the high-energy transmission grating spectrometer is most consistent with a cooling flow model, placing V426 Oph among the group of CVs including U Gem and EX Hya. An uninterrupted lightcurve was also constructed, in which we detect a significant 4.2 hr modulation together with its first harmonic at 2.1 hrs. Reanalysis of archival Ginga, and ROSAT X-ray lightcurves also reveals modulations at periods consistent with 4.2 and/or 2.1 hrs. Furthermore, optical photometry in V, simultaneous with the Chandra observation, indicates a modulation anti-correlated with the X-ray, and later more extensive R band photometry finds a signal at ~2.1 hrs. The earlier reported X-ray periods at ~0.5 and 1 hrs appear to be only transient and quasi-periodic in nature. In contrast, the 4.2 hr period or its harmonic are stable and persistent in X-ray/optical data from 1988 to 2003. This periodicity is clearly distinct from the 6.85 hr orbit, and could be due to the spin of the white dwarf. If this is the case, V426 Oph would be the first long period intermediate polar with a ratio P_spin/P_orb of 0.6. However, this interpretation requires unreasonable values of magnetic field strength and mass accretion rate.

arXiv comment11 pages, 7 figures, 5 tables. Accepted for publication in the Astrophysical Journal (to appear August 2004)

References in corpus (4)

• Two Types of X-ray Spectra in Cataclysmic Variables
• The Spin Period of EX Hydrae
• First Application of the Fe XVII I(17.10 A)/I(17.05 A) Line Ratio to Constrain the Plasma Density of a Cosmic X-ray Source
• Chandra Observations of the Dwarf Nova WX Hyi in Quiescence

Cited by in corpus (7)

• The defining characteristics of Intermediate Polars - the case of three candidate systems
• Dwarf nova oscillations and quasi-periodic oscillations in cataclysmic variables -- V. Results from an extensive survey
• Study of Fe K-alpha lines in Non-magnetic Cataclysmic Variables using Chandra HEG data
• X-ray Observations of the Bright Old Nova V603 Aquilae
• Testing the cooling flow model in the intermediate polar EX Hydrae
• X-ray spectroscopy in the microcalorimeter era 4: Optical depth effects on the soft X-rays studied with CLOUDY
• FUSE Observations of the Dwarf Nova SW UMa During Quiescence