An extended XMM-Newton observation of the Seyfert galaxy NGC 4051 - III. FeK emission and absorption

TL;DR

This study analyzes XMM-Newton data of NGC 4051, revealing complex Fe K absorption and emission features that indicate multiple velocity components in the ionized outflow, supporting models of shock interaction and cooling in AGN winds.

Contribution

It provides detailed spectral analysis of Fe K features, identifying two distinct velocity components and their variability, advancing understanding of AGN outflow dynamics and shock interactions.

Findings

Detection of two velocity components (~0.12c and 5000-7000 km/s) in the ionized absorber.

Fe K absorption lines vary with flux and luminosity, indicating dynamic outflow conditions.

Narrow Fe K emission line remains constant, with evidence of P Cygni profiles suggesting outflowing gas.

Abstract

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.