The impact of accretion disk winds on the X-ray spectrum of AGN: Part 1 - XSCORT

(abridged) The accretion disk in AGN is expected to produce strong outflows, in particular a UV-line driven wind. Despite providing a good fit to the data, current spectral models of the X-ray spectrum of AGN observed through an accretion disk wind are ad-hoc in their treatment of the properties of the wind material. In order to address these limitations we adopt a numerical computation method that links a series of radiative transfer calculations, incorporating the effect of a global velocity field in a self-consistent manner (XSCORT). We present a series of example spectra from the XSCORT code that allow us to examine the shape of AGN X-ray spectra seen through a wind, for a range of velocity and density distributions, total column densities and initial ionization parameters. These detailed spectral models clearly show considerable complexity and structure that is strongly affected by all these factors. The presence of sharp features in the XSCORT spectra contrasts strongly with both the previous models and with the smooth nature of the observed X-ray spectra of AGN with soft X-ray excesses, demonstrating that accretion disk winds are unlikely to be the origin of this mysterious spectral feature. The most significant parameter affecting the presence of the sharp features in the models is the terminal velocity of the wind. Increasing the terminal velocity of the absorbing material to ~c, and hence dramatically increasing the velocity dispersion across the wind, could potentially remove these features resulting in a spectrum similar to the previous models. Such a fast moving outflow cannot be associated with a radiatively driven accretion disk wind, however the presence of a highly relativistic jet may provide an origin for such material.Comment: 14 pages, 9 figures (colour), Accepted for publication in MNRAS (13th Aug 2007). Several significant changes to the text from v

Iron Kalpha emission from the low-luminosity Active Galaxies M81 and NGC 4579

We report on XMM-Newton spectroscopy of the low-luminosity active galaxies (LLAGN) M81 and NGC4579 both of which have known black hole masses and well-sampled spectral energy distributions (SED). The iron Kalpha line profiles from both the LLAGN can be described in terms of two components - a narrow line at 6.4 keV and a moderately broad line (FWHM = 20000 km/s) arising from highly ionized, He-like or H-like species (E \sim 6.8 keV). We interpret the broad lines arising from an accretion disk the inner edge of which is restricted to large radii (r_{in} \sim 100 r_g). However, the Eddington ratio, {L}/{L_{Edd}}, of these sources, is 3 - 4 orders of magnitude lower than that required to photo-ionize a cold disk to He-like iron. We suggest that the lines can be explained as collisionally ionized X-ray lines arising from the transition region between a hot (radiatively inefficient) flow in the inner regions and a cold disk outside r \sim 100r_g. The accretion flow geometry probed by our XMM-Newton observations is consistent with the truncated disk models proposed to explain the SED of LLAGNs.Comment: 8 pages, uses emulateapj5, To apear in Ap

The Location and Kinematics of the Coronal-Line Emitting Regions in Active Galactic Nuclei

We use the photoionization code CLOUDY to determine both the location and the kinematics of the optical forbidden, high-ionization line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km s-1. Iron-carrying grains are destroyed during this initial acceleration. This velocity is maintained by a balance between radiative forces and gravity in this super-Eddington source. Eventually the outflow is slowed at large radii by the gravitational forces of and interactions with the host galaxy. In this model, FHIL emission traces the transition between the active galactic nucleus (AGN) and bulge zones of influence

The messy environment of Mrk 6

In recent years it has become clear that understanding the absorption present in AGN is essential given its bearing on unification models. We present the most recent XMM-Newton observation of Mrk 6, with the goal of understanding the nature and origin of the complex absorption intrinsic to this source. X-ray spectral fitting shows that a simple warm absorption model provides an equally good statistical representation of the CCD data as a partial covering model. Furthermore, once the RGS data are included in the spectral fitting, the simple warm absorber model provides a very good fit to the data, without increasing the complexity of the model, in contrast with the partial covering model which requires the addition of either a low metalicity (<0.03 solar) thermal plasma or low temperature blackbody emission in order to provide a similar quality fit. The warm absorber is also a considerably more natural way to explain the variability observed in the X-ray absorbing column density between the previous XMM-Newton observation and this one, requiring only a second, higher column density, higher ionisation, absorber to be present during the previous XMM-Newton observation. In comparison, the partial covering models which requires moving, clumpy, material relatively close to the source that result in two distinct lines of sight, with separate absorbing columns that each vary considerably without any associated change in their covering fractions, in order to explain the observed variability. We associate the warm absorber either with an accretion disk wind with densities of ~10^9 /cm^3, or with an ionised `skin' or atmosphere of the molecular torus with densities of ~10^3 - 10^5 /cm^3.Comment: 11 pages, 8 figures. Accepted for publication by MNRAS 05/200

X-ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies

By combining complementary monitoring observations spanning long, medium and short time scales, we have constructed power spectral densities (PSDs) of six Seyfert~1 galaxies. These PSDs span $\gtrsim$4 orders of magnitude in temporal frequency, sampling variations on time scales ranging from tens of minutes to over a year. In at least four cases, the PSD shows a "break," a significant departure from a power law, typically on time scales of order a few days. This is similar to the behavior of Galactic X-ray binaries (XRBs), lower mass compact systems with breaks on time scales of seconds. NGC 3783 shows tentative evidence for a doubly-broken power law, a feature that until now has only been seen in the (much better-defined) PSDs of low-state XRBs. It is also interesting that (when one previously-observed object is added to make a small sample of seven), an apparently significant correlation is seen between the break time scale $T$ and the putative black hole mass $M_{\rm BH}$, while none is seen between break time scale and luminosity. The data are consistent with the linear relation T = M_{\rm BH}/10^{6.5} \Msun; extrapolation over 6--7 orders of magnitude is in reasonable agreement with XRBs. All of this strengthens the case for a physical similarity between Seyfert~1s and XRBs.Comment: 27 pages, 13 figures. Accepted for publication in ApJ. Typo correcte