Anatomy of the AGN in NGC 5548: II. The Spatial, Temporal and Physical   Nature of the Outflow from HST/COS Observations
  (Abridged) Our deep multiwavelength campaign on NGC 5548 revealed an unusually strong X-ray obscuration. The resulting dramatic decrease in incident ionizing flux allowed us to construct a comprehensive physical, spatial and temporal picture for the long-studied AGN wind in this object. Here we analyze the UV spectra of the outflow acquired during the campaign as well as from four previous epochs. We find that a simple model based on a fixed total column-density absorber, reacting to changes in ionizing illumination, matches the very different ionization states seen in five spectroscopic epochs spanning 16 years. Absorption troughs from C III* appeared for the first time during our campaign. From these troughs, we infer that the main outflow component is situated at 3.5+-1 pc from the central source. Three other components are situated between 5-70 pc and two are further than 100 pc. The wealth of observational constraints and the disparate relationship of the observed X-ray and UV flux between different epochs make our physical model a leading contender for interpreting trough variability data of quasar outflows. 
N. Arav, C. Chamberlain, G.A. Kriss, J.S. Kaastra, M. Cappi, M.   Mehdipour, P.-O. Petrucci, K.C. Steenbrugge, E. Behar, S. ...
astro-ph.GA