During a continuous 26 hour X-ray observation of the 98-min binary EX Hydrae using the CMA detector on EXOSAT, a 67-min modulation was detected with a pulse-fraction of about 30 per cent. The phase of the modulation coincides with that of the 67-min optical modulation which has a pulse-fraction of 15 per cent. The X-ray and optical pulse shapes are similar. A modulation with a period of 98 min is also found in a power spectral analysis of the EXOSAT data. This variation has an amplitude half that of the 67-min X-ray modulation. The 98-min phase-folded light curve is comprised of two features: a narrow, partial dip which corresponds to the duration and phase of a partial optical eclipse, and a broad, partial dip lasting about one-third of the 98-min cycle and centred 75° earlier than the narrow feature. An analysis of extensive optical data reveals that, in addition to the 67-min variation, there are two optical modulations with pulsed fractions of 5 per cent: one at half the orbital period, or 49.1 min, and one at 46.4 min. A moderate resolution (|λ/Δλ~10-50|) soft X-ray spectrum of EX Hydrae in the energy range 0.04–2 keV was also obtained during the observation through the use of an objective transmission grating. The spectrum exhibits excess flux at low energies relative to simple one-component continuum fits. An adequate fit can be obtained if one allows a fraction of the emitted flux (∼70–80 per cent) to be exposed to a high column density of absorbing material (|N_ H~1-3×10²¹⁻²|) with the remainder being relatively unabsorbed (|N_ H~10¹⁹⁻²|). Such a model may be appropriate if the emitting source is partially obscured by an intrinsic absorbing component.
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Córdova et al. (1985) studied this question.