An extended XMM-Newton observation of the Seyfert galaxy NGC 4051 - III.
  FeK emission and absorption
  An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009
detected a photo-ionized outflow with a complex absorption line velocity
structure and a broad correlation of velocity with ionization parameter, shown
in Pounds et al (2011) to be consistent with a highly ionized, high velocity
wind running into the interstellar medium or previous ejecta, losing much of
its kinetic energy in the resultant strong shock. In the present paper we
examine the Fe K spectral region in more detail and find support for two
distinct velocity components in the highly ionized absorber, with values
corresponding to the putative fast wind (~ 0.12c) and the post-shock flow (v ~
5000-7000 km/s). The Fe K absorption line structure is seen to vary on a
orbit-to-orbit timescale, apparently responding to both a short term increase
in ionizing flux and - perhaps more generally - to changes in the soft X-ray
(and simultaneous UV) luminosity. The latter result is particularly interesting
in providing independent support for the existence of shocked gas being cooled
primarily by Compton scattering of accretion disc photons. The Fe K emission is
represented by a narrow fluorescent line from near-neutral matter, with a weak
red wing modelled here by a relativistic diskline. The narrow line flux is
quasi-constant throughout the 45-day 2009 campaign, but is resolved, with a
velocity width consistent with scattering from a component of the post-shock
flow. Evidence for a P Cygni profile is seen in several individual orbit
spectra for resonance transitions in both Fe XXV and Fe XXVI.
