ASCAObservations of the Ionized Gas in the Seyfert Galaxy NGC 3783

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Abstract
We present the results from ASCA observations of NGC 3783 carried out during 1993 and 1996. Variability is observed both between the two epochs and within the individual observations, the latter due to a nonstationary process. We find the spectra at both epochs to contain features due to absorption by ionized material, predominantly due to O VII and O VIII. We find the opacity for such material to decrease by a factor ~2 in the ~0.7-1.0 keV band between the epochs while the photoionizing flux increases by ~25%. By comparison with detailed photoionization models we show that this behavior is inconsistent with that expected from a single zone of photoionized gas. A deficit in the data compared to such models, consistent with excess absorption by O VIII, supports the suggestion that the material consists of two or more zones. Significant Fe K shell emission is also observed during both epochs. We show that this emission is dominated by the asymmetric line profile expected from the innermost regions of the accretion flow. We find no evidence that the Fe emission varied in either shape or equivalent width between the two epochs.
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