2,602 research outputs found
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
Properties of AGN coronae in the NuSTAR era
The focussing optics of NuSTAR have enabled high signal-to-noise spectra to
be obtained from many X-ray bright Active Galactic Nuclei (AGN) and Galactic
Black Hole Binaries (BHB). Spectral modelling then allows robust
characterization of the spectral index and upper energy cutoff of the coronal
power-law continuum, after accounting for reflection and absorption effects.
Spectral-timing studies, such as reverberation and broad iron line fitting, of
these sources yield coronal sizes, often showing them to be small and in the
range of 3 to 10 gravitational radii in size. Our results indicate that coronae
are hot and radiatively compact, lying close to the boundary of the region in
the compactness - temperature diagram which is forbidden due to runaway pair
production. The coincidence suggests that pair production and annihilation are
essential ingredients in the coronae of AGN and BHB and that they control the
shape of the observed spectra.Comment: 11 pages, 8 figures, accepted for publication in MNRA
A Killing tensor for higher dimensional Kerr-AdS black holes with NUT charge
In this paper, we study the recently discovered family of higher dimensional
Kerr-AdS black holes with an extra NUT-like parameter. We show that the inverse
metric is additively separable after multiplication by a simple function. This
allows us to separate the Hamilton-Jacobi equation, showing that geodesic
motion is integrable on this background. The separation of the Hamilton-Jacobi
equation is intimately linked to the existence of an irreducible Killing
tensor, which provides an extra constant of motion. We also demonstrate that
the Klein-Gordon equation for this background is separable.Comment: LaTeX, 14 pages. v2: Typo corrected and equation added. v3: Reference
added, introduction expanded, published versio
The power output of local obscured and unobscured AGN: crossing the absorption barrier with Swift/BAT and IRAS
The Swift/BAT 9-month catalogue of active galactic nuclei (AGN) provides an
unbiased census of local supermassive black hole accretion, and probes to all
but the highest levels of absorption in AGN. We explore a method for
characterising the bolometric output of both obscured and unobscured AGN by
combining the hard X-ray data from Swift/BAT (14-195keV) with the reprocessed
IR emission as seen with the IRAS all-sky surveys. This approach bypasses the
complex modifications to the SED introduced by absorption in the optical, UV
and 0.1-10 keV regimes and provides a long-term, average picture of the
bolometric output of these sources. We broadly follow the approach of Pozzi et
al. for calculating the bolometric luminosities by adding nuclear IR and hard
X-ray luminosities, and consider different approaches for removing non-nuclear
contamination in the large-aperture IRAS fluxes. Using mass estimates from the
M_BH-L_bulge relation, we present the Eddington ratios \lambda_Edd and 2-10 keV
bolometric corrections for a subsample of 63 AGN (35 obscured and 28
unobscured) from the Swift/BAT catalogue, and confirm previous indications of a
low Eddington ratio distribution for both samples. Importantly, we find a
tendency for low bolometric corrections (typically 10-30) for the obscured AGN
in the sample (with a possible rise from ~15 for \lambda_Edd<0.03 to ~32 above
this), providing a hitherto unseen window onto accretion processes in this
class of AGN. This finding is of key importance in calculating the expected
local black hole mass density from the X-ray background since it is composed of
emission from a significant population of such obscured AGN. Analogous studies
with high resolution IR data and a range of alternative models for the torus
emission will form useful future extensions to this work. (Abridged)Comment: 19 pages, 16 figures, 2 tables. Accepted for publication in MNRA
The hard X-ray perspective on the soft X-ray excess
The X-ray spectra of many active galactic nuclei (AGN) exhibit a `soft
excess' below 1keV, whose physical origin remains unclear. Diverse models have
been suggested to account for it, including ionised reflection of X-rays from
the inner part of the accretion disc, ionised winds/absorbers, and
Comptonisation. The ionised reflection model suggests a natural link between
the prominence of the soft excess and the Compton reflection hump strength
above 10keV, but it has not been clear what hard X-ray signatures, if any, are
expected from the other soft X-ray candidate models. Additionally, it has not
been possible up until recently to obtain high-quality simultaneous
measurements of both soft and hard X-ray emission necessary to distinguish
these models, but upcoming joint XMM-NuSTAR programmes provide precisely this
opportunity. In this paper, we present an extensive analysis of simulations of
XMM+NuSTAR observations, using two candidate soft excess models as inputs, to
determine whether such campaigns can disambiguate between them by using hard
and soft X-ray observations in tandem. The simulated spectra are fit with the
simplest "observer's model" of a black body and neutral reflection to
characterise the strength of the soft and hard excesses. A plot of the strength
of the hard excess against the soft excess strength provides a diagnostic plot
which allows the soft excess production mechanism to be determined in
individual sources and samples using current state-of-the-art and next
generation hard X-ray enabled observatories. This approach can be
straightforwardly extended to other candidate models for the soft excess.Comment: 12 pages, 11 figures, accepted for publication in ApJ. Added
reference
Hidden Symmetry of Higher Dimensional Kerr-NUT-AdS Spacetimes
It is well known that 4-dimensional Kerr-NUT-AdS spacetime possesses the
hidden symmetry associated with the Killing-Yano tensor. This tensor is
"universal" in the sense that there exist coordinates where it does not depend
on any of the free parameters of the metric. Recently the general higher
dimensional Kerr-NUT-AdS solutions of the Einstein equations were obtained. We
demonstrate that all these metrics with arbitrary rotation and NUT parameters
admit a universal Killing-Yano tensor. We give an explicit presentation of the
Killing-Yano and Killing tensors and briefly discuss their properties.Comment: 4 pages, some discussion and references are adde
A study to evaluate the correlation between serological profile and histopathology of lupus nephritis.
INTRODUCTION
Systemic lupus erythematosus is an autoimmune disease of
unknown etiology, characterized by the involvement of multiple organ
systems . Organ damage is mediated by tissue binding autoantibodies
and immune complexes. The hallmark of SLE is the presence of serum
autoantibodies directed to nuclear constituents (i.e., antinuclear
antibodies, ANA). In most of the patients, these autoantibodies are
present for a few years before the first clinical symptoms appear. The
clinical presentation and course of SLE are extremely variable. Some
patients have spontaneous remissions; others may have mild
musculoskeletal involvement which responds to therapy and a few die
from progressive severe multisystem disease unresponsive to
immunosuppressive therapy. Lupus nephritis is one of the common manifestations of SLE. Diagnosis of SLE is based on the 11 criteria defined by American
Rheumatism Association (ARA). SLE patients develop wide range of
autoantibodies. SLE commonly involves skin, joints, kidneys, serosal surfaces including pleura and pericardium, CNS and hematopoietic system.
ANA is the most sensitive test for SLE and is present in more than 90% of patients but not specific for SLE. Anti dsDNA is a more specific but less sensitive marker of SLE. High titre of anti dsDNA correlates with disease activity and especially with lupus nephritis. Serum levels of complements C3 and C4 are usually
decreased in active SLE and in active lupus nephritis. Most of
the patients with active proliferative lupus nephritis have high titre of anti
dsDNA and low C3 and C4 levels. Nowadays renal biopsy is recommended in almost all patients who have clinical or laboratory evidence of renal involvement to determine the histological class of lupus nephritis and thereby to plan
therapy. But the requirement of renal biopsy has not been studied
scientifically so far. So this study aimed to look at the need for renal
biopsy in lupus nephritis scientifically.
AIMS & OBJECTIVES :
1. To evaluate the correlation between serological profile and
histopathology of lupus nephritis.
2. To find out the class of LN which has significant correlation with
serological profile.
3. To define the positive predictive value of anti dsDNA and low
complement levels with proliferative lupus nephritis.
4. To assess whether renal biopsy will alter the treatment plan in
proliferative lupus nephritis.
CONCLUSION :
• In our study, serological profile of SLE had significant correlation
with histopathology of lupus nephritis.
• Anti dsDNA, low C3 and low C4 had significant independent
correlation (p<0.05) with proliferative LN (class IV, IV&V).
• Positive predictive value of all these three serological markers put
together for proliferative LN was 97.4%.
• None of the patients with class II or class V LN had the
combination of anti dsDNA positivity, low C3 and low C4 levels.
• So, we may suggest that serology alone is sufficient to predict the
proliferative LN and there can be a case for starting
immunosuppressive therapy without biopsy in a known SLE
patient with evidence of LN and positive serology
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