16,051 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
Seyfert galaxies with Swift: giant flares, rapid drops, and other surprises
Swift has initiated a new era of understanding the extremes of active
galactic nuclei (AGN) variability, their drivers and underlying physics. This
is based on its rapid response, high sensitivity, good spatial resolution, and
its ability to collect simultaneously X--ray-to-optical SEDs. Here, we present
results from our recent monitoring campaigns with Swift of highly variable AGN,
including outbursts, deep low states, and unusual long-term trends in several
Seyfert galaxies including Mrk 335, WPVS007, and RXJ2314.9+2243. We also report
detection of a new X-ray and optical outburst of IC 3599 and our Swift
follow-ups. IC 3599 was previously known as one of the AGN with the
highest-amplitude outbursts. We briefly discuss implications of this second
outburst of IC 3599 for emission scenarios including accretion-disk
variability, repeat tidal disruption events, and the presence of a binary
supermassive black hole.Comment: to appear in "Swift: 10 years of discovery", Proceedings of Scienc
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
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.
XMM-Newton observation of the ULIRG NGC 6240: The physical nature of the complex Fe K line emission
We report on an XMM-Newton observation of the ultraluminous infrared galaxy
NGC 6240. The 0.3-10 keV spectrum can be successfully modelled with: (i) three
collisionally ionized plasma components with temperatures of about 0.7, 1.4,
and 5.5 keV; (ii) a highly absorbed direct power-law component; and (iii) a
neutral Fe K_alpha and K_beta line. We detect a significant neutral column
density gradient which is correlated with the temperature of the three plasma
components. Combining the XMM-Newton spectral model with the high spatial
resolution Chandra image we find that the temperatures and the column densities
increase towards the center.
With high significance, the Fe K line complex is resolved into three distinct
narrow lines: (i) the neutral Fe K_alpha line at 6.4 keV; (ii) an ionized line
at about 6.7 keV; and (iii) a higher ionized line at 7.0 keV (a blend of the Fe
XXVI and the Fe K_beta line). While the neutral Fe K line is most probably due
to reflection from optically thick material, the Fe XXV and Fe XXVI emission
arises from the highest temperature ionized plasma component.
We have compared the plasma parameters of the ultraluminous infrared galaxy
NGC 6240 with those found in the local starburst galaxy NGC 253. We find a
striking similarity in the plasma temperatures and column density gradients,
suggesting a similar underlying physical process at work in both galaxies.Comment: 8 pages including 9 figures. Accepted for publication in A&
X-ray Spectral and Variability Properties of Low-Mass AGN
We study the X-ray properties of a sample of 14 optically-selected low-mass
AGN whose masses lie within the range 1E5 -2E6 M(solar) with XMM-Newton. Only
six of these low-mass AGN have previously been studied with sufficient quality
X-ray data, thus, we more than double the number of low-mass AGN observed by
XMM-Newton with the addition of our sample. We analyze their X-ray spectral
properties and variability and compare the results to their more massive
counterparts. The presence of a soft X-ray excess is detectable in all five
objects which were not background dominated at 2-3 keV. Combined with previous
studies, this gives a total of 8 low-mass AGN with a soft excess. The low-mass
AGN exhibit rapid, short-term variability (hundreds to thousands of seconds) as
well as long-term variability (months to years). There is a well-known
anti-correlation between black hole mass and variability amplitude (normalized
excess variance). Comparing our sample of low-mass AGN with this relation we
find that all of our sample lie below an extrapolation of the linear relation.
Such a flattening of the relation at low masses (below about 1E6 M(solar)) is
expected if the variability in all AGN follows the same shape power spectrum
with a break frequency that is dependent on mass. Finally, we also found two
objects that show significant absorption in their X-ray spectrum, indicative of
type 2 objects, although they are classified as type 1 AGN based on optical
spectra.Comment: 12 pages, 5 figures, 7 tables, 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
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