1,000 research outputs found
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
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
Probing the face-on disc-corona system of the bare AGN Mrk 110 from UV to hard X-rays: A moderate changing-state AGN?
Context. The X-ray broadband spectra of the bare active galactic nucleus (AGN) Mrk 110, obtained by simultaneous XMM-Newton and NuSTAR observations performed in November 2019 and April 2020, are characterised by the presence of a prominent and absorption-free smooth soft X-ray excess, moderately broad O VII and Fe Kα emission lines, and a lack of a strong Compton hump. The disc-corona system is almost viewed face-on as inferred from the O VII accretion disc lines. While relativistic reflection as the sole emission is ruled out, a simplified combination of soft and hard Comptonisation (using COMPTT) from a warm and a hot corona, plus mild relativistic disc reflection (occuring at a few 10 s Rg) reproduces the data very well.Aims. We aim to confirm the physical origin of the soft X-ray excess of Mrk 110 and to determine its disc-corona system properties from its energetics using two new sophisticated models: REXCOR and RELAGN, respectively.Methods. We applied these models to the 0.3–79 keV X-ray broadband spectra and to the spectral energy distribution (SED) from UV to hard X-rays, respectively.Results. At both epochs, the inferred high values of the warm-corona heating from the X-ray broadband spectral analysis using REXCOR confirm that the soft X-ray excess of Mrk 110 mainly originates from a warm corona rather than relativistic reflection. The intrinsic best-fit SED determined at both epochs using RELAGN show a high X-ray contribution relative to the UV and are very well reproduced by a warm and hot corona plus mild relativistic reflection. The outer radii of the hot and warm corona are located at a few 10 s and ∼100 Rg, respectively. Moreover, combining the inferred low Eddington ratio (approximatively a few percent) from this work, and previous multi-wavelength spectral and timing studies suggest that Mrk 110 could be classified as a moderate changing-state AGN.Conclusions. Our analysis confirms the existence of a warm corona as a significant contribution to the soft X-ray excess and UV emission in Mrk 110, adding to growing evidence that AGN accretion deviates from standard disc theory. This strengthens the importance of long-term multi-wavelength monitoring on both single targets and large AGN surveys to reveal the real nature of the disc-corona system in AGNs
On why the Iron K-shell absorption in AGN is not a signature of the local Warm/Hot Intergalactic Medium
We present a comparison between the 2001 XMM-Newton and 2005 Suzaku
observations of the quasar, PG1211+143 at z=0.0809. Variability is observed in
the 7 keV iron K-shell absorption line (at 7.6 keV in the quasar frame), which
is significantly weaker in 2005 than during the 2001 XMM-Newton observation.
From a recombination timescale of <4 years, this implies an absorber density
n>0.004 particles/cm3, while the absorber column is 5e22<N_H <1 1e24
particles/cm2. Thus the sizescale of the absorber is too compact (pc scale) and
the surface brightness of the dense gas too high (by 9-10 orders of magnitude)
to arise from local hot gas, such as the local bubble, group or Warm/Hot
Intergalactic Medium (WHIM), as suggested by McKernan et al. (2004, 2005).
Instead the iron K-shell absorption must be associated with an AGN outflow with
mildly relativistic velocities. Finally we show that the the association of the
absorption in PG1211+143 with local hot gas is simply a coincidence, the
comparison between the recession and iron K absorber outflow velocities in
other AGN does not reveal a one to one kinematic correlation.Comment: accepted for publication in MNRAS LETTERS. 5 pages, 4 figure
Quantifying the fast outflow in the luminous Seyfert galaxy PG1211+143
We report two new XMM-Newton observations of PG1211+143 in December 2007,
again finding evidence of the fast outflow of highly ionised gas first detected
in 2001. Stacking the new spectra with those from two earlier XMM-Newton
observations reveals strong and broad emission lines of FeXXV and OVIII,
indicating the fast outflow to be persistent and to have a large covering
factor. This finding confirms a high mass rate for the ionised ouflow in
PG1211+143 and provides the first direct measurement of a wide angle,
sub-relativistic outflow from an AGN transporting mechanical energy with the
potential to disrupt the growth of the host galaxy. We suggest PG1211+143 may
be typical of an AGN in a rapid super-Eddington growth phase.Comment: Accepted for publication in MNRAS. Extended version with new figures
and table
Intensive HST, RXTE and ASCA Monitoring of NGC 3516: Evidence Against Thermal Reprocessing
During 1998 April 13-16, NGC 3516 was monitored almost continuously with HST
for 10.3 hr in the UV and 2.8 d in the optical, and simultaneous RXTE and ASCA
monitoring covered the same period. The X-rays were strongly variable with the
soft (0.5-2 keV) showing stronger variations (~65% peak-to-peak) than the hard
(2-10 keV; ~50% peak-to-peak). The optical continuum showed much smaller but
highly significant variations: a slow ~2.5% rise followed by a faster ~3.5%
decline. The short UV observation did not show significant variability.
The soft and hard X-ray light curves were strongly correlated with no
significant lag. Likewise, the optical continuum bands (3590 and 5510 A) were
also strongly correlated with no measurable lag above limits of <0.15 d.
However no significant correlation or simple relationship could be found for
the optical and X-ray light curves. These results appear difficult to reconcile
with previous reports of correlations between X-ray and optical variations and
of measurable lags within the optical band for some other Seyfert 1s.
These results also present serious problems for "reprocessing" models in
which the X-ray source heats a stratified accretion disk which then reemits in
the optical/ultraviolet: the synchronous variations within the optical would
suggest that the emitting region is <0.3 lt-d across, while the lack of
correlation between X-ray and optical variations would indicate, in the context
of this model, that any reprocessing region must be >1 lt-d in size. It may be
possible to resolve this conflict by invoking anisotropic emission or special
geometry, but the most natural explanation appears to be that the bulk of the
optical luminosity is generated by some other mechanism than reprocessing.Comment: 23 pages including 6 figures, accepted for publication in Ap
Ionized Absorbers in AGN: the Role of Collisional Ionization and Time-Evolving Photoionization
In this paper we explore collisional ionization and time-evolving
photoionization in the, X-ray discovered, ionized absorbers in Seyfert
galaxies. These absorbers show temporal changes inconsistent with simple
equilibrium models. We develop a simple code to follow the temporal evolution
of non-equilibrium photoionized gas. As a result several effects appear that
are easily observable; and which, in fact, may explain otherwise paradoxical
behavior.
Specifically we find that: 1) In many important astrophysical conditions pure
collisional and photoionization equilibria can be distinguished with moderate
spectral resolution observations, due to a strong absorption structure between
1 and 3 keV. 2) In time-evolving non-equilibrium photoionization models the
response of the ionization state of the gas to sudden changes of the ionizing
continuum is smoothed and delayed at low gas densities, even when the
luminosity increases. 3) If the changes of the ionizing luminosity are not
instantaneous, and the electron density is low enough (the limit depends on the
average ionization state of the gas), the ionization state of the gas can
continue to increase while the source luminosity decreases, so a maximum in the
ionization state of a given element may occur during a minimum of the ionizing
intensity (the opposite of the prediction of equilibrium models). 4) Different
ions of different elements reach their equilibrium configuration on different
time-scales.
These properties are similar to those seen in several ionized absorbers in
AGN, properties which had hitherto been puzzling. We applied these models to a
high S/N ROSAT PSPC observation of the Seyfert 1 galaxy NGC 4051.Comment: 36 pages, 10 figures, accepted for publication on Apj, in pres
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