82 research outputs found
Modélisation de la combustion turbulente des mélanges hétérogènes en richesse. Application au calcul d'une flamme stabilisée par l'élargissement brusque d'un canal bidimensionnel
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The Correlation between X-ray spectral slope and FeKalpha line energy in radio-quiet active galactic nuclei
A significant correlation between FeKalpha line energy and X-ray spectral
slope has been discovered among radio-quiet active galactic nuclei. The
ionization stage of the bulk of the FeKalpha emitting material is not the same
in all active galactic nuclei and is related to the shape of the X-ray
continua. Active galactic nuclei with a steep X-ray spectrum tend to have a
fluorescence FeKalpha line from highly ionized material. In the narrow-line
Seyfert 1 galaxies with steeper X-ray spectrum (Gamma_X > 2.1), the FeKalpha
line originates from highly ionized material. In the Seyfert 1 galaxies and
quasars with flatter X-ray spectrum (Gamma_X < 2.1), bulk of the FeKalpha
emission arises from near neutral or weakly ionized material. The correlation
is an important observational characteristic related to the accretion process
in radio quiet active galactic nuclei and is driven by a fundamental physical
parameter which is likely to be the accretion rate relative to the Eddington
rate.Comment: 4 pages, To apear in ApJ Letter
X-ray reflection in a sample of X-ray bright Ultraluminous X-ray sources
We apply a reflection-based model to the best available XMM-Newton spectra of
X-ray bright UltraLuminous X-ray (ULX) sources (NGC 1313 X-1, NGC 1313 X-2, M
81 X-6, Holmberg IX X-1, NGC 5408 X-1 and Holmberg II X-1). A spectral drop is
apparent in the data of all the sources at energies 6-7 keV. The drop is
interpreted here in terms of relativistically-blurred ionized reflection from
the accretion disk. A soft-excess is also detected from these sources (as
usually found in the spectra of AGN), with emission from O K and Fe L, in the
case of NGC 5408 X-1 and Holmberg II X-1, which can be understood as features
arising from reflection of the disk. Remarkably, ionized disk reflection and
the associated powerlaw continuum provide a good description of the broad-band
spectrum, including the soft-excess. There is no requirement for thermal
emission from the inner disk in the description of the spectra. The black holes
of these systems must then be highly spinning, with a spin close to the maximum
rate of a maximal spinning black hole. The results require the action of strong
light bending in these sources. We suggest that they could be strongly
accreting black holes in which most of the energy is extracted from the flow
magnetically and released above the disc thereby avoiding the conventional
Eddington limit.Comment: Accepted for publication in MNRA
Revisit Short Term X-ray Spectral Variability of NGC 4151 with Chandra
We present new X-ray spectral data for the Seyfert 1 nucleus in NGC 4151
observed with Chandra for 200 ks. A significant ACIS pileup is present,
resulting in a non-linear count rate variation during the observation. With
pileup corrected spectral fitting, we are able to recover the spectral
parameters and find consistency with those derived from unpiled events in the
ACIS readout streak and outer region from the bright nucleus. The absorption
corrected 2-10 keV flux of the nucleus varied between 6E-11 and 1E-10 erg
s^{-1} cm^{-2}. Similar to earlier Chandra studies of NGC 4151 at a historical
low state, the photon indices derived from the same absorbed power-law model
are \Gamma~0.7-0.9. However, we show that \Gamma is highly dependent on the
adopted spectral models. Fitting the power-law continuum with a Compton
reflection component gives \Gamma~1.1. By including passage of non-uniform
X-ray obscuring clouds, we can reproduce the apparent flat spectral states with
\Gamma~1.7, typical for Seyfert 1 AGNs. The same model also fits the hard
spectra from previous ASCA "long look" observation of NGC 4151 in the lowest
flux state. The spectral variability during our observation can be interpreted
as variations in intrinsic soft continuum flux relative to a Compton reflection
component that is from distant cold material and constant on short time scale,
or variations of partially covering absorber in the line of sight towards the
nucleus. An ionized absorber model with ionization parameter \log\xi ~ 0.8-1.1
can also fit the low-resolution ACIS spectra. If the partial covering model is
correct, adopting a black hole mass M_{BH} ~ 4.6E+7 Msun we constrain the
distance of the obscuring cloud from the central black hole to be r<~9
light-days, consistent with the size of broad emission line region of NGC 4151
from optical reverberation mapping.Comment: Accepted to ApJ. 41 pages, 11 figures, and 4 tables
Estrogen regulation of TRPM8 expression in breast cancer cells
<p>Abstract</p> <p>Background</p> <p>The calcium-permeable cation channel TRPM8 (melastatin-related transient receptor potential member 8) is over-expressed in several cancers. The present study aimed at investigating the expression, function and potential regulation of TRPM8 channels by ER alpha (estrogen receptor alpha) in breast cancer.</p> <p>Methods</p> <p>RT-PCR, Western blot, immuno-histochemical, and siRNA techniques were used to investigate TRPM8 expression, its regulation by estrogen receptors, and its expression in breast tissue. To investigate the channel activity in MCF-7 cells, we used the whole cell patch clamp and the calcium imaging techniques.</p> <p>Results</p> <p>TRPM8 channels are expressed at both mRNA and protein levels in the breast cancer cell line MCF-7. Bath application of the potent TRPM8 agonist Icilin (20 μM) induced a strong outwardly rectifying current at depolarizing potentials, which is associated with an elevation of cytosolic calcium concentration, consistent with established TRPM8 channel properties. RT-PCR experiments revealed a decrease in TRPM8 mRNA expression following steroid deprivation for 48 and 72 hours. In steroid deprived medium, addition of 17-beta-estradiol (E<sub>2</sub>, 10 nM) increased both TRPM8 mRNA expression and the number of cells which respond to Icilin, but failed to affect the Ca<sup>2+ </sup>entry amplitude. Moreover, silencing ERα mRNA expression with small interfering RNA reduced the expression of TRPM8. Immuno-histochemical examination of the expression of TRPM8 channels in human breast tissues revealed an over-expression of TRPM8 in breast adenocarcinomas, which is correlated with estrogen receptor positive (ER<sup>+</sup>) status of the tumours.</p> <p>Conclusion</p> <p>Taken together, these results show that TRPM8 channels are expressed and functional in breast cancer and that their expression is regulated by ER alpha.</p
A long, hard look at MCG-6-30-15 with XMM-Newton II: detailed EPIC analysis and modelling
The bright Seyfert 1 galaxy MCG-6-30-15 has provided some of the best
evidence to date for the existence of supermassive black holes in active
galactic nuclei. Observations with ASCA revealed an X-ray iron line profile
shaped by strong Doppler and gravitational effects. In this paper the shape of
the iron line, its variability characteristics and the robustness of this
spectral interpretation are examined using the long XMM-Newton observation
taken in 2001. A variety of spectral models, both including and excluding the
effects of strong gravity, are compared to the data in a uniform fashion. The
results strongly favour models in which the spectrum is shaped by emission from
a relativistic accretion disc. It is far more difficult to explain the 3-10 keV
spectrum using models dominated by absorption (either by warm or partially
covering cold matter), emission line blends, curved continua or additional
continuum components. These provide a substantially worse fit to the data and
fail to explain other observations (such as the simultaneous BeppoSAX
spectrum). This reaffirms the veracity of the relativistic `disc line'
interpretation. The short term variability in the shape of the energy spectrum
is investigated and explained in terms of a two-component emission model. Using
a combination of spectral variability analyses the spectrum is successfully
decomposed into a variable power-law component (PLC) and a reflection dominated
component (RDC). The former is highly variable while the latter is
approximately constant throughout the observation, leading to the well-known
spectral variability patterns. (Abridged)Comment: 25 pages. 24 figures. Accepted for publication in MNRA
An X-ray Spectral Survey of Radio-Loud AGN With ASCA
We present a uniform and systematic analysis of the 0.6-10 keV X-ray spectra
of radio-loud active galactic nuclei (AGN) observed by ASCA. The sample 10
BLRGs, 5 QSRs, 9 NLRGs, and 10 RGs. At soft X-rays, about half of the NLRGs and
all of the RGs exhibit a thermal plasma component, with a bimodal distribution
of temperatures and luminosities, suggesting an origin either in a surrounding
cluster or loose group or in a hot corona. At energies above 2 keV, a hard
power-law component is detected in 90% of cases. The power-law photon indices
and luminosities in BLRGs, QSRs, and NLRGs are similar, consistent with
orientation-based unification schemes. Significant excess cold absorption is
detected in most NLRGs, but also in some BLRGS and QSRs, which was somewhat
unexpected. In contrast to Seyfert galaxies, only one object showss the
signature of a warm absorber. The nuclear X-ray luminosity is correlated with
the luminosity of the [O III] emission line, the FIR emission at 12 microns,
and the lobe radio power at 5 GHz. The Fe K line is detected in 50% of BLRGs,
one QSR, and a handful of NLRGs. This sample also includes 6 Weak Line Radio
Galaxies (WLRGs). Their spectra WLRGs can be generally decomposed into a soft
thermal component with hard absrorbed power-law component, which is
significantly flatter than any other radio-loud AGNs. Their intrinsic
luminosities are two orders of magnitude lower than in other sources of the
sample. An interesting possibility is that WLRGs represent an extreme
population of radio galaxies in which the central black hole is accreting at a
rate well below the Eddington rate.Comment: To appear in the Astrophysical Journal. 72 pages, including many
tables and figures. Fig 1 is separate, in TIFF format. Postscript version of
fig 1 and postscript version of entire preprint can be obtained from
http://www.astro.psu.edu/users/mce/preprint_index.htm
An X-ray Spectral Model for Compton-Thick Toroidal Reprocessors
The central engines of both type 1 and type 2 AGNs are thought to harbor a
toroidal structure that absorbs and reprocesses high-energy photons from the
central X-ray source. If the reprocessor is Compton-thick, the calculation of
emission-line and continuum spectra that are suitable for direct fitting to
X-ray data is challenging because the reprocessed emission depends on the
spectral shape of the incident continuum, which may not be directly observable.
We present new Monte-Carlo calculations of Green's functions for a toroidal
reprocessor that provide significant improvements over currently available
models. The Green's function approach enables the construction of X-ray
spectral fitting models that allow arbitrary incident spectra as part of the
fitting process. The calculations are fully relativistic and have been
performed for column densities that cover the Compton-thin to Compton-thick
regime, for incident photon energies up to 500 keV. The reprocessed continuum
and fluorescent line emission due to Fe Ka, Fe Kb, and Ni Ka are treated
self-consistently, eliminating the need for ad hoc modeling that is currently
common practice. We find that the spectral shape of the Compton-thick
reflection spectrum in both the soft and hard X-ray bands in our toroidal
geometry is different compared to that obtained from disk models. A key result
of our study is that a Compton-thick toroidal structure that subtends the same
solid angle at the X-ray source as a disk can produce a reflection spectrum
that is ~6 times weaker than that from a disk. This highlights the widespread
and erroneous interpretation of the so-called "reflection-fraction" as a solid
angle, obtained from fitting disk-reflection models to Compton-thick sources
without regard for proper consideration of geometry. (Abridged)Comment: 19 pages, 11 figures, 1 table. Accepted for publication in MNRA
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
Expression of TRPC6 channels in human epithelial breast cancer cells
<p>Abstract</p> <p>Background</p> <p>TRP channels have been shown to be involved in tumour generation and malignant growth. However, the expression of these channels in breast cancer remains unclear. Here we studied the expression and function of endogenous TRPC6 channels in a breast cancer cell line (MCF-7), a human breast cancer epithelial primary culture (hBCE) and in normal and tumour breast tissues.</p> <p>Methods</p> <p>Molecular (Western blot and RT-PCR), and immunohistochemical techniques were used to investigate TRPC6 expression. To investigate the channel activity in both MCF-7 cells and hBCE we used electrophysiological technique (whole cell patch clamp configuration).</p> <p>Results</p> <p>A non selective cationic current was activated by the oleoyl-2-acetyl-sn-glycerol (OAG) in both hBCE and MCF-7 cells. OAG-inward current was inhibited by 2-APB, SK&F 96365 and La<sup>3+</sup>. TRPC6, but not TRPC7, was expressed both in hBCE and in MCF-7 cells. TRPC3 was only expressed in hBCE. Clinically, TRPC6 mRNA and protein were elevated in breast carcinoma specimens in comparison to normal breast tissue. Furthermore, we found that the overexpression of TRPC6 protein levels were not correlated with tumour grades, estrogen receptor expression or lymph node positive tumours.</p> <p>Conclusion</p> <p>Our results indicate that TRPC6 channels are strongly expressed and functional in breast cancer epithelial cells. Moreover, the overexpression of these channels appears without any correlation with tumour grade, ER expression and lymph node metastasis. Our findings support the idea that TRPC6 may have a role in breast carcinogenesis.</p
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