A SEARCH FOR PERIODICITIES IN THE X-RAY-EMISSION FROM CATACLYSMIC VARIABLES

We present the results of a search for periodicities in the X-ray emission from cataclysmic variables observed with the Einstein Observatory's IPC. The search was conducted in the energy band 0.16-3.5 keV and covered the frequency range 0.01-2.5 Hz. We show power spectra for 51 observations of 31 systems and derive upper limits to the pulse fractions of signals that are not detected. We find that the majority of systems show no coherent periodicities in their X-ray emission, which is consistent with a model in which the X-rays are produced in a disk/white dwarf boundary layer. The X-ray emission from AE Aqr is found to be modulated with a period of 33.08 s, which agrees with the period found in its optical light, and in GK Per we find evidence of higher harmonics of the 351 s oscillations detected by EXOSAT. The objects V603 Aql and SU UMa can be considered candidate magnetic systems, based on the periodicities found, but further observations are needed for confirmation.