CHANDRA OBSERVATION OF V426 OPHIUCHI: WEIGHING THE EVIDENCE FOR A MAGNETIC WHITE DWARf

摘要

We report the results of a 45 ks Chandra observation of the cataclysmic variable (CV) 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 light curve was also constructed, in which we detect a significant 4.2 hr modulation together with its first harmonic at 2.1 hr. Reanalysis of archival Ginga and ROSAT X-ray light curves also reveals modulations at periods consistent with 4.2 and/or 2.1 hr. Furthermore, optical photometry in V, simultaneous with the Chandra observation, indicates a modulation anticorrelated with the X-ray, and later more extensive R-band photometry finds a signal at ～2.1 hr. The earlier reported X-ray periods at ～0.5 and 1 hr appear to be only transient and quasi-periodic in nature. In contrast, the 4.2 hr period or its harmonic is 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.