We present a high signal-to-noise ROSAT position sensitive proportional counter (PSPC) observation of the Seyfert 1 galaxy NGC 3783. The 0.1-2.5 keV spectrum shows strong evidence for an absorption edge most likely associated with O VII-VIII. Such a feature, which has now been detected in a number of PSPC spectra (Nandra et al.; Nandra & Pounds; Turner et al.), is the signature of highly ionized material, the so-called warm absorber, in the line of sight to the X-ray source. The result is strongly supported by analysis of previously unpublished Ginga data and reanalysis of a 1985 EXOSAT observation of NGC 3783. We show that the warm absorber is plausibly located at a radius ≲1018 cm from the X-ray source, possibly in an outflowing wind.
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Turner et al. (1993) studied this question.