16,617 research outputs found
Investigating the nature of narrow-line Seyfert 1 galaxies with high-energy spectral complexity
(abridged) With the commissioning of XMM came the discovery of 2.5-10 keV
spectral complexity in some narrow-line Seyfert 1 galaxies (NLS1). In this
work, we define two samples of NLS1: a complex sample whose members exhibit
high-energy complexity (C-sample), and a general sample of NLS1 whose 2.5-10
keV spectra do not strongly deviate from a simple power law (S-sample).
Considering historical light curves of each object we find that the C-sample is
representative of NLS1 in a low X-ray flux state, whereas the members of the
S-sample appear to be in a typical flux state. Moreover, from measurements of
alpha_ox with contemporaneous UV/X-ray data, we find that the C-sample of NLS1
appear X-ray weaker at the time of the observation. For two NLS1 in the
C-sample multi-epoch measurements of alpha_ox are available and suggest that
alpha_ox approaches more normal values as the complexity between 2.5-10 keV
diminishes. This implies that a source could transit from one sample to the
other as its X-ray flux varies. Secondly, there are indications that the
C-sample sources, on average, exhibit stronger optical FeII emission, with the
three most extreme (FeII/H_beta > 1.8) FeII emitters all displaying complexity
in the 2.5-10 keV band. However, it is not clear if the possible connection
between FeII strength and spectral complexity is due to the FeII producing
mechanism or because strong FeII emitters may exhibit the greatest variability
and consequently more likely to be caught in an extreme (low) flux state. Based
on the current analysis it we can not straightforwardly dismiss absorption or
reflection as the cause of the X-ray complexity.Comment: 8 pages, 3 figures. Accepted for publication in MNRA
X-rays from the radio-quiet quasar PG 1407+265: relativistic jet or accretion disc emission?
We present two XMM-Newton observations of the luminous (L_x > 10^46 erg/s),
radio-quiet quasar, PG 1407+265, separated by eleven months. The data indicate
two distinct states: a highly variable, bright state (first epoch); and a
quiescent, low-flux one (second epoch). During the low-flux state the spectrum
is consistent with a single, unabsorbed power law. However, during the brighter
state a highly variable, steep component is statistically required.
Contemporaneous UV data from the Optical Monitor allow an estimate of the
optical-to-X-ray spectral index (alpha_ox), which appears typical of
radio-quiet quasars during the low-flux state, but extremely flat during the
high-flux state. The XMM-Newton data can be described as originating from a
combination of jet and accretion disc processes, in which the (relativistic)
X-ray jet only works intermittently. The scenario could help describe some of
the complexities seen in the broadband spectral energy distribution of PG
1407+265, such as weak high-ionisation emission lines, strong Fe II, unbeamed
continuum, and the weak radio emission relative to the optical.Comment: 9 pages, 8 figures. Accepted for publication in MNRAS. Correction
made to reported aox value. No changes in conclusion
The origin of blue-shifted absorption features in the X-ray spectrum of PG 1211+143: Outflow or disc?
In some radio-quiet active galaxies (AGN), high-energy absorption features in
the x-ray spectra have been interpreted as Ultrafast Outflows (UFOs) -- highly
ionised material (e.g. Fe XXV and Fe XXVI) ejected at mildly relativistic
velocities. In some cases, these outflows can carry energy in excess of the
binding energy of the host galaxy. Needless to say, these features demand our
attention as they are strong signatures of AGN feedback and will influence
galaxy evolution. For the same reason, alternative models need to be discussed
and refuted or confirmed. Gallo & Fabian proposed that some of these features
could arise from resonance absorption of the reflected spectrum in a layer of
ionised material located above and corotating with the accretion disc.
Therefore, the absorbing medium would be subjected to similar blurring effects
as seen in the disc. A priori, the existence of such plasma above the disc is
as plausible as a fast wind. In this work, we highlight the ambiguity by
demonstrating that the absorption model can describe the ~7.6 keV absorption
feature (and possibly other features) in the quasar PG 1211+143, an AGN that is
often described as a classic example of an UFO. In this model, the 2-10 keV
spectrum would be largely reflection dominated (as opposed to power law
dominated in the wind models) and the resonance absorption would be originating
in a layer between about 6 and 60 gravitational radii. The studies of such
features constitutes a cornerstone for future X-ray observatories like Astro-H
and Athena+. Should our model prove correct, or at least important in some
cases, then absorption will provide another diagnostic tool with which to probe
the inner accretion flow with future missions.Comment: 4 pages. Accepted for publication in MNRAS Letter
How well can we measure supermassive black hole spin?
Being one of only two fundamental properties black holes possess, the spin of
supermassive black holes (SMBHs) is of great interest for understanding
accretion processes and galaxy evolution. However, in these early days of spin
measurements, consistency and reproducibility of spin constraints have been a
challenge. Here we focus on X-ray spectral modelling of active galactic nuclei
(AGN), examining how well we can truly return known reflection parameters such
as spin under standard conditions. We have created and fit over 4000 simulated
Seyfert 1 spectra each with 3751k counts. We assess the fits with
reflection fraction of = 1 as well as reflection-dominated AGN with =
5. We also examine the consequence of permitting fits to search for retrograde
spin. In general, we discover that most parameters are over-estimated when
spectroscopy is restricted to the 2.5 - 10.0 keV regime and that models are
insensitive to inner emissivity index and ionization. When the bandpass is
extended out to 70keV, parameters are more accurately estimated. Repeating the
process for = 5 reduces our ability to measure photon index (3 to 8
per cent error and overestimated), but increases precision in all other
parameters -- most notably ionization, which becomes better constrained
(45 erg cm ) for low ionization parameters (200 erg
cm ). In all cases, we find the spin parameter is only well
measured for the most rapidly rotating supermassive black holes (i.e.
0.8 to about 0.10) and that inner emissivity index is never well
constrained. Allowing our model to search for retrograde spin did not improve
the results.Comment: Accepted for publication in MNRAS. 13 pages, 7 figure
Driving extreme variability: The evolving corona and evidence for jet launching in Markarian 335
Variations in the X-ray emission from the narrow line Seyfert 1 galaxy,
Markarian 335 (Mrk 335), are studied on both long and short timescales through
observations made between 2006 and 2013 with XMM-Newton, Suzaku and NuSTAR.
Changes in the geometry and energetics of the corona that give rise to this
variability are inferred through measurements of the relativistically blurred
reflection seen from the accretion disc. On long timescales, we find that
during the high flux epochs the corona has expanded, covering the inner regions
of the accretion disc out to a radius of 26(-7,+10)rg. The corona contracts to
within 12rg and 5rg in the intermediate and low flux epochs, respectively.
While the earlier high flux observation made in 2006 is consistent with a
corona extending over the inner part of the accretion disc, a later high flux
observation that year revealed that the X-ray source had become collimated into
a vertically-extended jet-like corona and suggested relativistic motion of
material upward. On short timescales, we find that an X-ray flare during a low
flux epoch in 2013 corresponded to a reconfiguration from a slightly extended
corona to one much more compact, within just 2~3rg of the black hole. There is
evidence that during the flare itself, the spectrum softened and the corona
became collimated and slightly extended vertically as if a jet-launching event
was aborted. Understanding the evolution of the X-ray emitting corona may
reveal the underlying mechanism by which the luminous X-ray sources in AGN are
powered.Comment: 21 pages, 9 figures. Accepted for publication in MNRA
Is HE 0436-4717 Anemic? A deep look at a bare Seyfert 1 galaxy
A multi-epoch, multi-instrument analysis of the Seyfert 1 galaxy HE 0436-4717
is conducted using optical to X-ray data from XMM-Newton and Swift (including
the BAT). Fitting of the UV-to-X-ray spectral energy distribution shows little
evidence of extinction and the X-ray spectral analysis does not confirm
previous reports of deep absorption edges from OVIII. HE 0436-4717 is a "bare"
Seyfert with negligible line-of-sight absorption making it ideal to study the
central X-ray emitting region. Three scenarios were considered to describe the
X-ray data: partial covering absorption, blurred reflection, and soft
Comptonization. All three interpretations describe the 0.5-10.0 keV spectra
well. Extrapolating the models to 100 keV results in poorer fits for the the
partial covering model. When also considering the rapid variability during one
of the XMM-Newton observations, the blurred reflection model appears to
describe all the observations in the most self-consistent manner. If adopted,
the blurred reflection model requires a very low iron abundance in HE
0436-4717. We consider the possibilities that this is an artifact of the
fitting process, but it appears possible that it is intrinsic to the object.Comment: 7 tables, 11 figures, 16 pages; accepted for publication in MNRAS 17
Feb. 201
Probing the geometry and motion of AGN coronae through accretion disc emissivity profiles
To gain a better understanding of the inner disc region that comprises active
galactic nuclei it is necessary to understand the pattern in which the disc is
illuminated (the emissivity profile) by X-rays emitted from the continuum
source above the black hole (corona). The differences in the emissivity
profiles produced by various corona geometries are explored via general
relativistic ray tracing simulations. Through the analysis of various
parameters of the geometries simulated it is found that emissivity profiles
produced by point source and extended geometries such as cylindrical slabs and
spheroidal coronae placed on the accretion disc are distinguishable. Profiles
produced by point source and conical geometries are not significantly
different, requiring an analysis of reflection fraction to differentiate the
two geometries. Beamed point and beamed conical sources are also simulated in
an effort to model jet-like coronae, though the differences here are most
evident in the reflection fraction. For a point source we determine an
approximation for the measured reflection fraction with the source height and
velocity. Simulating spectra from the emissivity profiles produced by the
various geometries produce distinguishable differences. Overall spectral
differences between the geometries do not exceed 15 per cent in the most
extreme cases. It is found that emissivity profiles can be useful in
distinguishing point source and extended geometries given high quality spectral
data of extreme, bright sources over long exposure times. In combination with
reflection fraction, timing, and spectral analysis we may use emissivity
profiles to discern the geometry of the X-ray source.Comment: 15 pages, 12 figures. Accepted for publication in MNRA
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