  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.
