EXOSAT soft X-ray observations of EX Hydrae.

Abstract

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. 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.