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

摘要

We report the results of a 45 ks Chandra observation of the cataclysmicvariable V426 Ophiuchus. The high resolution spectrum from the high-energytransmission grating spectrometer is most consistent with a cooling flow model,placing V426 Oph among the group of CVs including U Gem and EX Hya. Anuninterrupted lightcurve was also constructed, in which we detect a significant4.2 hr modulation together with its first harmonic at 2.1 hrs. Reanalysis ofarchival Ginga, and ROSAT X-ray lightcurves also reveals modulations at periodsconsistent with 4.2 and/or 2.1 hrs. Furthermore, optical photometry in V,simultaneous with the Chandra observation, indicates a modulationanti-correlated with the X-ray, and later more extensive R band photometryfinds a signal at ~2.1 hrs. The earlier reported X-ray periods at ~0.5 and 1hrs appear to be only transient and quasi-periodic in nature. In contrast, the4.2 hr period or its harmonic are stable and persistent in X-ray/optical datafrom 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 Ophwould be the first long period intermediate polar with a ratio P_spin/P_orb of0.6. However, this interpretation requires unreasonable values of magneticfield strength and mass accretion rate.