Highly Ionized X-ray Absorbers in AGNs and their Energetic: the case of NGC 4051

Highly ionized absorbers are found in 50% of type 1 Seyferts and QSOs. They presence, along our line of sight, imprints a number of absorption lines from highly ionized metals in the far UV and X-ray spectral bands, like FeX-XVII, CIV-VI, OVI-OVIII, NeVII-X, etc. These absorption lines are always detected blue-shifted compared to the host galaxy reference system, which implies that the ionized material is being ejected from the nucleus and driven outwards, possibly by the AGN radiation pressure. Outflow velocities span a wide range, from few hundreds to few thousands km/s in the so called Narrow-Absorption Line (NAL) and/or Warm Absorber objects, to non negligible fractions of the speed of light in UV Broad Absorption Line (BAL) or X-ray Ultra-Fast Outflows (UFOs). These outflows are believed to be photo-ionized by the central source and their energetic depends on their mass outflow rate which, in turn, depends on the volume density n_e of the material, which is difficult to measure because degenerate with the square of the distance R of the absorber from the photo-ionizing source.
In this talk, after a brief overview of the phenomenon, I will show how time-evolving photo-ionization works and how it can be used to break the degeneracy between the absorber volume density n_e and its distance R from the central engine. I will then present the particularly fortunate case of NGC 4051 and show the puzzling results of the analysis performed here at OAR of the long 2009 XMM-Newton monitoring of this source.