paper

The Ionized Nuclear Environment in NGC 985 as seen by Chandra and BeppoSAX

arXiv:astro-ph/0409490 · doi:10.1086/425293

Abstract

(Abridged) We investigate the ionized environment of the Seyfert 1 galaxy NGC 985 with a new Chandra-HETGS observation and an archival BeppoSAX observation. Two absorption components are clearly required to fit absorption features observed in the Chandra spectrum. The components have a difference of 29 in ionization parameter and 3 in column density. The presence of the low ionization component is evidenced by an Fe M-shell unresolved transition array (UTA) produced by charge states VII to XIII. The high ionization phase is required by the presence of broad absorption features arising from several blends of Fe L-shell transitions (Fe XVII-XXII). A third highly ionized component might also be present, but the data does not allow to constrain its properties. An X-ray luminosity variation by a factor 2.3 is observed between the BeppoSAX and Chandra observations (separated by almost 3 years). Variability in the opacity of the absorbers is detected in response to the continuum variation, but while the colder component is consistent with a simple picture of photoionization equilibrium, the ionization state of the hotter component seems to increase while the continuum flux drops. The most striking result in our analysis is that during both the Chandra and the BeppoSAX observations, the two absorbing components appear to have the same pressure. Thus, we suggest that the absorption arises from a multi-phase wind. Such scenario can explain the change in opacity of both absorption components during the observations, but requires that a third hotter component is pressure-confining the two phases. Hence, our analysis points to a 3-phase medium similar to the wind found in NGC 3783, and further suggests that such a wind might be a common characteristic in AGN.

arXiv commentAccepted for publication in ApJ. 6 tables and 17 figures

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