A SEARCH FOR THE 2-OMEGA OMEGA FREQUENCY IN THE X-RAY LIGHT CURVES OF INTERMEDIATE POLARS

Wynn & King have shown that discless accretion gives rise to modulations at either the omega - OMEGA or 2omega - OMEGA frequencies in the X-ray light curves of intermediate polars. However, the EXOSAT archive shows no sign of a 2omega - OMEGA modulation in any of the systems observed. An omega - OMEGA modulation larger than haff the spin-pulse amplitude has been seen only once, while generally the omega - OMEGA pulses are weak or absent. Unless the spin periods are misidentified, this implies that the intermediate polars accrete predominantly, though in some systems not exclusively, through discs.