16,884 research outputs found
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
Caught in the act: Measuring the changes in the corona that cause the extreme variability of 1H 0707-495
The X-ray spectra of the narrow line Seyfert 1 galaxy, 1H 0707-495, obtained
with XMM-Newton, from time periods of varying X-ray luminosity are analysed in
the context of understanding the changes to the X-ray emitting corona that lead
to the extreme variability seen in the X-ray emission from active galactic
nuclei (AGN). The emissivity profile of the accretion disc, illuminated by the
X-ray emitting corona, along with previous measurements of reverberation time
lags are used to infer the spatial extent of the X-ray source. By fitting a
twice-broken power law emissivity profile to the relativistically-broadened
iron K fluorescence line, it is inferred that the X-ray emitting corona expands
radially, over the plane of the accretion disc, by 25 to 30 per cent as the
luminosity increases, contracting again as the luminosity decreases, while
increases in the measured reverberation lag as the luminosity increases would
require also variation in the vertical extent of the source above the disc. The
spectrum of the X-ray continuum is found to soften as the total X-ray
luminosity increases and we explore the variation in reflected flux as a
function of directly-observed continuum flux. These three observations combined
with simple, first-principles models constructed from ray tracing simulations
of extended coron self-consistently portray an expanding corona whose average
energy density decreases, but with a greater number of scattering particles as
the luminosity of this extreme object increases.Comment: 12 pages, 4 figures. Accepted for publication in MNRA
Modelling the Extreme X-ray Spectrum of IRAS 13224-3809
The extreme NLS1 galaxy IRAS 13224-3809 shows significant variability,
frequency depended time lags, and strong Fe K line and Fe L features in the
long 2011 XMM-Newton observation. In this work we study the spectral properties
of IRAS 13224-3809 in detail, and carry out a series of analyses to probe the
nature of the source, focusing in particular on the spectral variability
exhibited. The RGS spectrum shows no obvious signatures of absorption by
partially ionised material (warm absorbers). We fit the 0.3-10.0 keV spectra
with a model that includes relativistic reflection from the inner accretion
disc, a standard powerlaw AGN continuum, and a low-temperature (~0.1 keV)
blackbody, which may originate in the accretion disc, either as direct or
reprocessed thermal emission. We find that the reflection model explains the
time-averaged spectrum well, and we also undertake flux-resolved and
time-resolved spectral analyses, which provide evidence of gravitational
light-bending effects. Additionally, the temperature and flux of the blackbody
component are found to follow the relation expected for simple
thermal blackbody emission from a constant emitting area, indicating a physical
origin for this component.Comment: 12 pages, 7 figures, accepted for publication in MNRA
Slow dynamics of a confined supercooled binary mixture II: Q space analysis
We report the analysis in the wavevector space of the density correlator of a
Lennard Jones binary mixture confined in a disordered matrix of soft spheres
upon supercooling. In spite of the strong confining medium the behavior of the
mixture is consistent with the Mode Coupling Theory predictions for bulk
supercooled liquids. The relaxation times extracted from the fit of the density
correlator to the stretched exponential function follow a unique power law
behavior as a function of wavevector and temperature. The von Schweidler
scaling properties are valid for an extended wavevector range around the peak
of the structure factor. The parameters extracted in the present work are
compared with the bulk values obtained in literature.Comment: 8 pages with 8 figures. RevTeX. Accepted for publication in Phys.
Rev.
Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1
X-ray spectral timing analysis is presented of XMM-Newton observations of the
narrow line Seyfert 1 galaxy I Zwicky 1 (I Zw 1) taken in 2015 January. After
exploring the effect of background flaring on timing analyses, X-ray time lags
between the reflection-dominated 0.3-1.0keV energy and continuum-dominated
1.0-4.0keV band are measured, indicative of reverberation off the inner
accretion disc. The reverberation lag time is seen to vary as a step function
in frequency; across lower frequency components of the variability, 3e-4 to
1.2e-3Hz a lag of 160s is measured, but the lag shortens to (59 +/- 4)s above
1.2e-3Hz. The lag-energy spectrum reveals differing profiles between these
ranges with a change in the dip showing the earliest arriving photons. The low
frequency signal indicates reverberation of X-rays emitted from a corona
extended at low height over the disc while at high frequencies, variability is
generated in a collimated core of the corona through which luminosity
fluctuations propagate upwards. Principal component analysis of the variability
supports this interpretation, showing uncorrelated variation in the spectral
slope of two power law continuum components. The distinct evolution of the two
components of the corona is seen as a flare passes inwards from the extended to
the collimated portion. An increase in variability in the extended corona was
found preceding the initial increase in X-ray flux. Variability from the
extended corona was seen to die away as the flare passed into the collimated
core leading to a second sharper increase in the X-ray count rate.Comment: 18 pages, 11 figures. Accepted for publication in MNRA
Radiating black hole solutions in Einstein-Gauss-Bonnet gravity
In this paper, we find some new exact solutions to the Einstein-Gauss-Bonnet
equations. First, we prove a theorem which allows us to find a large family of
solutions to the Einstein-Gauss-Bonnet gravity in -dimensions. This family
of solutions represents dynamic black holes and contains, as particular cases,
not only the recently found Vaidya-Einstein-Gauss-Bonnet black hole, but also
other physical solutions that we think are new, such as, the Gauss-Bonnet
versions of the Bonnor-Vaidya(de Sitter/anti-de Sitter) solution, a global
monopole and the Husain black holes. We also present a more general version of
this theorem in which less restrictive conditions on the energy-momentum tensor
are imposed. As an application of this theorem, we present the exact solution
describing a black hole radiating a charged null fluid in a Born-Infeld
nonlinear electrodynamics
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