86 research outputs found
Turkdean Roman Villa, Gloucestershire: archaeological investigations 1997-1998
Before the transmission of the first ‘live’ Time Team television programme on 23 August 1997, the existence of a Roman villa near Chalkhill Barn in the parish of Turkdean, 12 miles north-east of Cirencester and 2 miles from the Fosse Way, was hardly known to the archaeological community (FIG. 1). That a Roman building did exist in this location had, however, been suspected for a number of years by the landowner, the late Mr Wilf Mustoe. Distinctive linear parchmarks suggestive of buildings had been clearly visible at ground level in the grass pasture each dry summer, and in 1976 Mr Mustoe made a measured sketch plan of them on the back of an envelope. Subsequently the sketch was drawn up into a scale plan entitled ‘Roman villa’ by Simon Goddard, a relation. There was little knowledge of the site outside of Mr Mustoe's family until it was independently ‘discovered’ by local archaeologist Roger Box in August 1996 whilst fortuitously flying over the site in a helicopter. In the evening light Mr Box instantly recognised the parchmarks of an unmistakable Roman villa and took a series of photographs (FIG. 2). Mr Box showed his photographs to Mr Mustoe, and with his agreement wrote to Time Team suggesting that this would be an excellent site for a television programme. Arrangements were duly set in place and the evidence of the cropmarks was confirmed by a trial geophysical survey in March 199
CAIXA: a Catalogue of AGN In the XMM-Newton Archive II. Multiwavelength correlations
We presented CAIXA, a Catalogue of AGN in the XMM-Newton Archive, in a
companion paper. Here, a systematic search for correlations between the X-ray
spectral properties and the multiwavelength data was performed for the sources
in CAIXA. All the significant (>99.9% confidence level) correlations are
discussed along with their physical implications on current models of AGN. Two
main correlations are discussed in this paper: a) a very strong
anti-correlation between the FWHM of the H optical line and the ratio
between the soft and the hard X-ray luminosity. Although similar
anti-correlations between optical line width and X-ray spectral steepness have
already been discussed in the literature (see e.g., Laor et al. 1994, Boller et
al. 1996, Brandt et al. 1997), we consider the formulation we present in this
paper is more fundamental, as it links model-independent quantities. Coupled
with a strong anti-correlation between the V to hard X-ray flux ratio and the
H FHWM, it supports scenarios for the origin of the soft excess in AGN,
which require strong suppression of the hard X-ray emission; b) a strong (and
expected) correlation between the X-ray luminosity and the black hole mass. Its
slope, flatter than 1, is consistent with Eddington ratio-dependent bolometric
corrections, such as that recently proposed by Vasudevan & Fabian (2009).
Moreover, we critically review through various statistical tests the role that
distance biases play in the strong radio to X-ray luminosity correlation found
in CAIXA and elsewhere; we conclude that only complete, unbiased samples (such
as that recently published by Behar & Laor, 2008) should be used to draw
observational constraints on the origin of radio emission in radio-quiet AGN.Comment: 12 pages, 11 figures, accepted for publication in Astronomy and
Astrophysics; two figures erroneously attached by astroph to the paper were
remove
An XMM-Newton view of the `bare' nucleus of Fairall 9
We present the spectral results from a 130 ks observation, obtained from the
X-ray Multi-Mirror Mission-Newton (XMM-Newton) observatory, of the type I
Seyfert galaxy Fairall 9. An X-ray hardness-ratio analysis of the light-curves,
reveals a `softer-when-brighter' behaviour which is typical for radio-quiet
type I Seyfert galaxies. Moreover, we analyse the high spectral-resolution data
of the reflection grating spectrometer and we did not find any significant
evidence supporting the presence of warm-absorber in the low X-ray energy part
of the source's spectrum. This means that the central nucleus of Fairall 9 is
`clean' and thus its X-ray spectral properties probe directly the physical
conditions of the central engine. The overall X-ray spectrum in the 0.5-10 keV
energy-range, derived from the EPIC data, can be modelled by a relativistically
blurred disc-reflection model. This spectral model yields for Fairall 9 an
intermediate black-hole best-fit spin parameter of
.Comment: Accepted for publication in MNRAS. The paper contains 11 figures and
1 tabl
The XMM-Newton Wide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN
We discuss the broad band X-ray properties of one of the largest samples of
X-ray selected type-1 AGN to date (487 objects in total), drawn from the
XMM-Newton Wide Angle Survey. The objects cover 2-10 keV luminosities from
~10^{42}-10^{45} erg s^{-1} and are detected up to redshift ~4. We constrain
the overall properties of the broad band continuum, soft excess and X-ray
absorption, along with their dependence on the X-ray luminosity and redshift
and we discuss the implications for models of AGN emission. We constrained the
mean spectral index of the broad band X-ray continuum to =1.96+-0.02
with intrinsic dispersion sigma=0.27_{-0.02}^{+0.01}. The continuum becomes
harder at faint fluxes and at higher redshifts and luminosities. The dependence
of Gamma with flux is likely due to undetected absorption rather than to
spectral variation. We found a strong dependence of the detection efficiency of
objects on the spectral shape which can have a strong impact on the measured
mean continuum shapes of sources at different redshifts and luminosities. We
detected excess absorption in ~3% of our objects, with column densities ~a few
x10^{22} cm^{-2}. The apparent mismatch between the optical classification and
X-ray properties of these objects is a challenge for the standard AGN
unification model. We found that the fraction of objects with detected soft
excess is ~36%. Using a thermal model, we constrained the soft excess mean
temperature and intrinsic dispersion to ~100 eV and sigma~34 eV. The origin
of the soft excess as thermal emission from the accretion disk or Compton
scattered disk emission is ruled out on the basis of the temperatures detected
and the lack of correlation of the measured temperature with the X-ray
luminosity (abridged).Comment: 13 pages, 24 figures, Accepted for publication in Astronomy and
Astrophysic
The X-ray spectral properties of the AGN population in the XMM-Newton bright serendipitous survey
We present here a detailed X-ray spectral analysis of the AGN belonging to
the XMM-Newton bright survey (XBS) that comprises more than 300 AGN up to
redshift ~ 2.4. We performed an X-ray analysis following two different
approaches: by analyzing individually each AGN X-ray spectrum and by
constructing average spectra for different AGN types. From the individual
analysis, we find that there seems to be an anti correlation between the
spectral index and the sources' hard X-ray luminosity, such that the average
photon index for the higher luminosity sources (> 10E44 erg/s) is significantly
flatter than the average for the lower luminosity sources. We also find that
the intrinsic column density distribution agrees with AGN unified schemes,
although a number of exceptions are found (3% of the whole sample), which are
much more common among optically classified type 2 AGN. We also find that the
so-called "soft-excess", apart from the intrinsic absorption, constitutes the
principal deviation from a power-law shape in AGN X-ray spectra and it clearly
displays different characteristics, and likely a different origin, for
unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we
find that it is best reproduced by a combination of an unabsorbed (absorbed)
power law, a narrow Fe Kalpha emission line and a small (large) amount of
reflection for unabsorbed (absorbed) sources. We do not significantly detect
any relativistic contribution to the line emission and we compute an upper
limit for its equivalent width (EW) of 230 eV at the 3 sigma confidence level.
Finally, by dividing the type 1 AGN sample into high- and low-luminosity
sources, we marginally detect a decrease in the narrow Fe Kalpha line EW and in
the amount of reflection as the luminosity increases, the "so-called"
Iwasawa-Taniguchi effect.Comment: 42 pages, 15 figures, accepted for publication in Astronomy and
Astrophysic
Erratum: Studying the relationship between X-ray emission and accretion in AGNs using theXMM–NewtonBright Serendipitous Survey
We study the link between the X-ray emission in radio-quiet active galactic nuclei (AGN) and the accretion rate on the central supermassive black hole using a statistically well-defined and representative sample of 71 type 1 AGN extracted from the XMM–Newton Bright Serendipitous Survey. We search and quantify the statistical correlations between some fundamental parameters that characterize the X-ray emission, i.e. the X-ray spectral slope, Γ, and the X-ray ‘loudness’, and the accretion rate, both absolute (Ṁ) and normalized to the Eddington luminosity (Eddington ratio, λ). We parametrize the X-ray loudness using three different quantities: the bolometric correction Kbol, the two-point spectral index αOX and the disc/corona luminosity ratio. We find that the X-ray spectral index depends on the normalized accretion rate while the ‘X-ray loudness’ depends on both the normalized and the absolute accretion rate. The dependence on the Eddington ratio, in particular, is probably induced by the Γ – λ correlation. The two proxies usually adopted in the literature to quantify the X-ray loudness of an AGN, i.e. Kbol and αOX, behave differently, with Kbol being more sensitive to the Eddington ratio and αOX having a stronger dependence with the absolute accretion. The explanation of this result is likely related to the different sensitivity of the two parameters to the X-ray spectral index
X-ray Absorption and Reflection in Active Galactic Nuclei
X-ray spectroscopy offers an opportunity to study the complex mixture of
emitting and absorbing components in the circumnuclear regions of active
galactic nuclei, and to learn about the accretion process that fuels AGN and
the feedback of material to their host galaxies. We describe the spectral
signatures that may be studied and review the X-ray spectra and spectral
variability of active galaxies, concentrating on progress from recent Chandra,
XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for
absorption covering a wide range of column densities, ionization and dynamics,
and discuss the growing evidence for partial-covering absorption from data at
energies > 10 keV. Such absorption can also explain the observed X-ray spectral
curvature and variability in AGN at lower energies and is likely an important
factor in shaping the observed properties of this class of source.
Consideration of self-consistent models for local AGN indicates that X-ray
spectra likely comprise a combination of absorption and reflection effects from
material originating within a few light days of the black hole as well as on
larger scales. It is likely that AGN X-ray spectra may be strongly affected by
the presence of disk-wind outflows that are expected in systems with high
accretion rates, and we describe models that attempt to predict the effects of
radiative transfer through such winds, and discuss the prospects for new data
to test and address these ideas.Comment: Accepted for publication in the Astronomy and Astrophysics Review. 58
pages, 9 figures. V2 has fixed an error in footnote
Changes in Inflammatory Biomarkers Across Weight Classes in a Representative US Population: A Link Between Obesity and Inflammation
Obesity has been linked with a chronic state of inflammation which may be involved in the development of metabolic syndrome, cardiovascular disease, non-alcoholic steatohepatitis, and even cancer. The objective of this study was to examine the association between obesity class and levels of inflammatory biomarkers from men and women who participated in the 1999–2004 National Health and Nutrition Examination Survey (NHANES).
Serum concentrations of C-reactive protein (CRP) and fibrinogen were measured among US participants of the 1999–2004 NHANES. We examined biomarker levels across different weight classes with normal weight, overweight, and obesity classes 1, 2, and 3 were defined as BMI of <25.0, 25.0–29.9, 30.0–34.9, 35.0–39.9, and ≥40.0, respectively.
With CRP levels for normal weight individuals as a reference, CRP levels nearly doubled with each increase in weight class: +0.11 mg/dl (95% CI, 0.06–0.16) for overweight, +0.21 mg/dl (95% CI, 0.16–0.27) for obesity class 1, +0.43 mg/dl (95% CI, 0.26–0.61) for obesity class 2, and +0.73 mg/dl (95% CI, 0.55–0.90) for obesity class 3. With normal weight individuals as a reference, fibrinogen levels increase with increasing weight class and were highest for obesity class 3 individuals, +93.5 mg/dl (95% CI, 72.9–114.1). Individuals with hypertension or diabetes have higher levels of CRP and fibrinogen levels compared to individuals without hypertension or diabetes, even when stratified according to BMI.
There is a direct association between increasing obesity class and the presence of obesity-related comorbidities such as diabetes and hypertension with high levels of inflammatory biomarkers
Event trees and epistemic uncertainty in long‐term volcanic hazard assessment of Rift Volcanoes: the example of Aluto (Central Ethiopia)
Aluto is a peralkaline rhyolitic caldera located in a highly populated area in central Ethiopia. Its postcaldera eruptive activity has mainly consisted of self‐similar, pumice‐cone‐building eruptions of varying size and vent location. These eruptions are explosive, generating hazardous phenomena that could impact proximal to distal areas from the vent. Volcanic hazard assessments in Ethiopia and the East African Rift are still limited in number. In this study, we develop an event tree model for Aluto volcano. The event tree is doubly useful: It facilitates the design of a conceptual model for the volcano and provides a framework to quantify volcanic hazard. We combine volcanological data from past and recent research at Aluto, and from a tool to objectively derive analog volcanoes (VOLCANS), to parameterize the event tree, including estimates of the substantial epistemic uncertainty. Results indicate that the probability of a silicic eruption in the next 50 years is highly uncertain, ranging from 2% to 35%. This epistemic uncertainty has a critical influence on event‐tree estimates for other volcanic events, like the probability of occurrence of pyroclastic density currents (PDCs) in the next 50 years. The 90% credible interval for the latter is 5–16%, considering only the epistemic uncertainty in conditional eruption size and PDC occurrence, but 2–23% when adding the epistemic uncertainty in the probability of eruption in 50 years. Despite some anticipated challenges, we envisage that our event tree could be translated to other rift volcanoes, making it an important tool to quantify volcanic hazard in Ethiopia and elsewhere
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