69 research outputs found
A Suzaku Observation of MCG-2-58-22: Constraining the Geometry of the Circumnuclear Material
We have analyzed a Suzaku long-look of the active galactic nucleus
MCG-2-58-22, a type 1.5 Seyfert with very little X-ray absorption in the line
of sight and prominent features arising from reflection off circumnuclear
material: the Fe line and Compton reflection hump. We place tight constraints
on the power law photon index (Gamma=1.80+/-0.02), the Compton reflection
strength (R=0.69+/-0.05), and the Fe K emission line energy centroid and width
(E=6.40+/-0.02 keV, v_FWHM < 7100 km/s). We find no significant evidence for
emission from strongly ionized Fe, nor for a strong, relativistically broadened
Fe line, indicating that perhaps there is no radiatively efficient accretion
disk very close in to the central black hole. In addition we test a new
self-consistent physical model from Murphy & Yaqoob, the "MYTorus" model,
consisting of a donut-shaped torus of material surrounding the central
illuminating source and producing both the Compton hump and the Fe K line
emission. From the application of this model we find that the observed spectrum
is consistent with a Compton-thick torus of material (column density
NH=3.6(+1.3/-0.8) x 10^24 cm^-2) lying outside of the line of sight to the
nucleus, leaving it bare of X-ray absorption in excess of the Galactic column.
We calculate that this material is sufficient to produce all of the Fe line
flux without the need for any flux contribution from additional Compton-thin
circumnuclear material.Comment: 7 pages, 4 figures, 2 table
Granularity of the Diffuse Background Observed
First results are reported from a program for measuring the field-to-field fluctuation level of the cosmic diffuse background by using differences between the two background positions of each deep exposure with the High Energy X-ray Timing Experiment (HEXTE) instrument on the Remote X Ray Timing Explorer (RXTE). With 8 million live seconds accumulated to date a fluctuation level on the 15-25 keV band is observed which is consistent with extrapolations from the High Energy Astrophysical Observatory-1 (HEAO-1) measurements. Positive results are expected eventually at higher energies. Models of (active galactic nuclei) AGN origin will eventually be constrained by this program
Cosmic Ray Generation by Quasar Remnants: Constraints and Implications
The quasar remnant cores of nearby giant elliptical galaxies NGC 4486 (M87),
NGC 1399, NGC 4649 and NGC 4472 are the sites of supermassive (greater than one
billion solar masses) black holes. These objects are investigated as to the
viability of the conjecture that they could harbor compact dynamos capable of
generating the highest energy cosmic rays. For an accretion process involving
an equipartition magnetic field near the event horizons of the underlying
putative spun-up black holes, the energy achievable in accelerating protons
could well be greater or equal than 100 EeV for all these when only considering
the drag induced by curvature radiation. Estimates of the SED (spectral energy
distribution) of ambient core photons lead to the conclusion that the energy
losses arising from photo-pion production in proton collisions with these
target photons are relatively small for all but M87. For M87, the ambient
photon field is likely to be a limiting factor. Accretion rates on the order of
one solar mass per year, comparable to the Bondi rates and to the stellar mass
loss rates, are associated with (greater than 100 EeV) cosmic ray generation in
the other (electromagnetically dark) galactic core sites. If these sites are
found to be sources of such cosmic rays, it would suggest the presence of a
global inflow of interstellar gas all the way into the center of the host
galaxy.Comment: 11 pages Latex, no figures, uses mn and amssymb style files, accepted
for publication in MNRA
Flow cytometric measurement of STAT5 phosphorylation in cytomegalovirus-stimulated T cells
Cytomegalovirus (CMV)-specific T cells expand with CMV reactivation and are probably prerequisite for control and protection. Given the critical role STAT5A phosphorylation (pSTAT5A) in T cell proliferation, this study presents a simple and sensitive flow cytometric-based pSTAT5A assay to quickly identify CMV-specific T cell proliferation. We determined pSTAT5A in T cells treated with CMV-specific peptide mix (pp65 + IE1 peptides) from 20 healthy adult subjects and three immunodeficient patients with CARMIL-2 mutation. After stimulation, the percentage of pSTAT5A+ T cells in CMV-seropositive (CMV+) subjects significantly increased from 3.0% ± 1.9% (unstimulated) to 11.4% ± 5.9% (stimulated) for 24 h. After 7 days of stimulation, the percentage of expanded T cells amounted to 26% ± 17.2%. Conversely, the percentage of pSTAT5A+ T cells and T cell proliferation from CMV-seronegative (CMV−) subjects hardly changed (from 3.0% ± 1.3% to 3.7% ± 1.8% and from 4.3% ± 2.1% to 5.7% ± 1.7%, respectively). We analyzed the correlation between the percentage of pSTAT5A+ T cells versus (1) CMV-IgG concentrations versus (2) the percentage of expanded T cells and versus (3) the percentage of initial CMV-specific T cells. In immunodeficient patients with CARMIL-2 mutation, CMV-specific pSTAT5A and T cell proliferation were completely deficient. In conclusion, flow cytometric-based pSTAT5A assay represents an appropriate tool to quickly identify CMV-specific T cell proliferation and helps to understand dysfunctions in controlling other pathogens. Flow cytometric-based pSTAT5A assay may be a useful test in clinical practice and merits further validation in large studies
Starburst Galaxies and the X-Ray Background
Integrated X-ray spectra of an evolving population of starburst galaxies
(SBGs) are determined based on the observed spectra of local SBGs. In addition
to emission from hot gas and binary systems, our model SBG spectrum includes a
nonthermal component from Compton scattering of relativistic electrons by the
intense ambient far-IR and the (steeply evolving) CMB radiation fields. We use
these integrated spectra to calculate the levels of contribution of SBGs to the
cosmic X-ray background assuming that their density evolves as (1+z)^q up to a
maximal redshift of 5. We find that at energies <10 keV this contribution is at
a level of few percent for q up to 3, and in the range of 5%-15% for q ~ 4.5.
The Compton component is predicted to be the main SBG emission at high
energies, and its relative contribution gets progressively higher for
increasing redshift.Comment: 10 pages, 5 figures; accepted for publication in A&
Tracing the Warm Hot Intergalactic Medium in the local Universe
We present a simple method for tracing the spatial distribution and
predicting the physical properties of the Warm-Hot Intergalactic Medium (WHIM),
from the map of galaxy light in the local universe. Under the assumption that
biasing is local and monotonic we map the ~ 2 Mpc/h smoothed density field of
galaxy light into the mass density field from which we infer the spatial
distribution of the WHIM in the local supercluster. Taking into account the
scatter in the WHIM density-temperature and density-metallicity relation,
extracted from the z=0 outputs of high-resolution and large box size
hydro-dynamical cosmological simulations, we are able to quantify the
probability of detecting WHIM signatures in the form of absorption features in
the X-ray spectra, along arbitrary directions in the sky. To illustrate the
usefulness of this semi-analytical method we focus on the WHIM properties in
the Virgo Cluster region.Comment: 16 pages 11 Figures. Discussion clarified, alternative methods
proposed. Results unchanged. MNRAS in pres
An absorption origin for the X-ray spectral variability of MCG-6-30-15
The Seyfert I galaxy MCG-6-30-15 shows one of the best examples of a broad
"red wing" of emission in its X-ray spectrum at energies 2 < E < 6.4 keV,
commonly interpreted as being caused by relativistically-blurred reflection
close to the event horizon of the black hole. We aim to test an alternative
model in which absorption creates the observed spectral shape, explains the
puzzling lack of variability of the red wing and reduces the high reflection
albedo, substantially greater than unity, that is otherwise inferred at
energies E > 20 keV. We compiled all the available long-exposure, high-quality
data for MCG-6-30-15: 522 ks of Chandra HETGS, 282 ks of XMM-Newton pn/RGS and
253 ks of Suzaku XIS/PIN data. This is the first analysis of this full dataset.
We investigated the spectral variability on timescales >20 ks using principal
components analysis and fitted spectral models to "flux state" and mean spectra
over the energy range 0.5-45 keV (depending on detector). The absorber model
was based on the zones previously identified in the high-resolution grating
data. Joint fits were carried out to any data that were simultaneous. Multiple
absorbing zones covering a wide range of ionisation are required by the grating
data, including a highly ionised outflowing zone. A variable partial-covering
zone plus absorbed low-ionisation reflection, distant from the source, provides
a complete description of the variable X-ray spectrum. A single model fits all
the data. We conclude that these zones are responsible for the red wing, its
apparent lack of variability, the absorption structure around the Fe K-alpha
line, the soft-band "excess" and the high flux seen in the hard X-ray band. A
relativistically-blurred Fe line is not required in this model. We suggest the
partial covering zone is a clumpy wind from the accretion disk.Comment: Accepted for publication in Astronomy and Astrophysics. Corrected
versio
Investigating the reflection contribution to the X-ray emission of Ton S180
There is now growing evidence that the soft X-ray excess is almost ubiquitous
among unobscured active galaxies. In spite of the various interpretations that
have been considered in the last years, the nature of this foremost spectral
feature is not firmly established yet. In this context, we review from a
reflection perspective the three highest-quality X-ray observations of the
narrow-line Seyfert 1 galaxy Tonantzintla S180, obtained by XMM-Newton and
Suzaku. The X-ray spectrum of Ton S180 shows only moderate variations over a
time span of several years, suggesting that the same physical process accounts
for the bulk of the broad-band X-ray emission at the different epochs, and that
the properties of the X-ray source are fairly stable. We have successfully
applied in our spectral analysis a dual-reflector model, consisting of two
separate components: one arises from the surface of the accretion disc, is
highly ionized and blurred by relativistic effects; the other is cold, quite
faint, and can be associated with a distant reprocessor. Due to the strength
and the nearly power-law shape of its soft excess emission, Ton S180 is one of
the most challenging sources to test the X-ray reflection scenario. In this
work we provide a clear illustration of the great potential and spectral
flexibility of blurred reflection models, while discussing some of their
current limitations and possible shortcomings.Comment: 9 pages, 4 figures, 3 tables. Accepted for publication in MNRA
Small-Scale Fluctuations in Cosmic X-ray Background : A Power Spectrum Approach
Equations to investigate fluctuations in cosmic X-ray background radiation
due to point-like sources at high-redshift are formulated in a systematic way.
The angular power spectrum of X-ray background fluctuations is investigated
from large-scales to small-scales in various cosmological models such as open
universe models and models with the cosmological constant, assuming a simple
evolution model of the sources. The effect of epoch-dependent bias is
demonstrated for small-angle fluctuations. The contribution from shot noise
fluctuations is also discussed.Comment: 12 pages, 4 figures, Phys.Rev.D in pres
The spectrum of the cosmic X-ray background observed by RTXE/PCA
We have analyzed a large set of RXTE/PCA scanning and slewing observations
performed between April 1996 and March 1999. We obtained the 3-20 keV spectrum
of the cosmic X-ray background (CXB) by subtracting Earth-occulted observations
from observations of the X-ray sky at high galactic latitude and far away from
sources. The sky coverage is approximately ~22600 sq.deg. The PCA spectrum of
CXB in 3-20 keV energy band is adequately approximated by a single power law
with photon index Gamma~1.4 and normalization at 1 keV ~9.5 phot/s/cm2/keV/sr.
Instrumental background uncertainty precludes accurate RXTE/PCA measurements of
the spectrum of cosmic X-ray background at energies above 15 keV and therefore
we can not detect the high energy cutoff observed by HEAO-1 A2 experiment. Deep
observations of the 6 high latitude points used to model the PCA background
provide a coarse measure of the spatial variation of the CXB. The CXB
variations are consistent with a fixed spectral shape and variable
normalization characterized by a fractional rms amplitude of ~7% on angular
scales of ~1 square deg.Comment: 6 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysic
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