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.
Highlights
An extended XMM–Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009 found a rich absorption-line spectrum indicating a photoionized outflow with a wide range of velocities and ionization parameters (Pounds & Vaughan 2011a, hereafter Paper I)
If the Tombesi et al (2010) findings are confirmed, with highly ionized outflows at v ∼ 0.1c being relatively common in bright nearby galaxies, perhaps Eddington or mildly super-Eddington accretion is more common than generally believed. [A case for active galactic nucleus (AGN) black hole masses being overestimated has recently been argued by King 2010b.]
That issue is raised when we explore the variability of the Fe K profile and find evidence for P Cygni emission associated with the stronger absorption lines
Summary
An extended XMM–Newton observation of the Seyfert 1 galaxy NGC 4051 in 2009 found a rich absorption-line spectrum indicating a photoionized outflow with a wide range of velocities and ionization parameters (Pounds & Vaughan 2011a, hereafter Paper I). The absorption-line velocity structure and a broad correlation of velocity with ionization parameter were shown to be consistent with an outflow scenario where a highly ionized, high-velocity wind, perhaps launched during intermittent super-Eddington accretion (King & Pounds 2003), runs into the interstellar medium or previous ejecta, losing much of its kinetic energy in the resultant strong shock. C 2012 The Authors Monthly Notices of the Royal Astronomical Society C 2012 RAS thereby limiting further star formation and black hole growth. Such a momentum-driven feedback mechanism has been shown by King (2003, 2005) to reproduce the observed correlation of black hole and bulge mass If the Tombesi et al (2010) findings are confirmed, with highly ionized outflows at v ∼ 0.1c being relatively common in bright nearby galaxies, perhaps Eddington or mildly super-Eddington accretion is more common than generally believed. [A case for active galactic nucleus (AGN) black hole masses being overestimated has recently been argued by King 2010b.]
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