Abstract
The analysis of a 32-hr GINGA observation of the intermediate polar FO Aqr is presented. The power spectrum of the X-ray light curve, constructed using the one-dimensional CLEAN algorithm, indicates strong modulation at the binary-orbital, white-dwarf spin and beat periods. The asymmetry between the positive and negative orbital sidebands of the spin frequency implies that the beat modulation cannot be caused by an amplitude modulation of the spin pulse and must be intrinsic to the source. It is demonstrated that the beat is unlikely to be due to a reflection effect and as a result can only arise in a discless accretion geometry in which the majority of the accretion flow switches from one magnetic pole of the white dwarf to the other every half a beat cycle. This naturally produces an apparent orbital modulation of the X-ray spin pulse, which is seen clearly in these data
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