460 research outputs found
Accretion flow diagnostics with X-ray spectral-timing: the hard state of SWIFT J1753.5-0127
(Abridged) Recent XMM-Newton studies of X-ray variability in the hard states
of black hole X-ray binaries (BHXRBs) imply that the variability is generated
in the 'standard' optically-thick accretion disc. The variability originates in
the disc as mass-accretion fluctuations and propagates through the disc to
'light up' inner disc regions, eventually modulating the power-law emission
that is produced relatively centrally.
We present a comparative spectral-timing study of XMM-Newton data from the
BHXRB SWIFT J1753.5-0127 in a bright 2009 hard state with that from the
significantly fainter 2006 hard state, to show for the first time the change in
disc spectral-timing properties associated with a global increase in both the
accretion rate and the relative contribution of the disc emission to the
bolometric luminosity.
We show that, although there is strong evidence for intrinsic disc
variability in the more luminous hard state, the disc variability amplitude is
suppressed relative to that of the power-law emission, which contrasts with the
behaviour at lower luminosities where the disc variability is slightly enhanced
when compared with the power-law variations. In the higher-luminosity data, the
disc variability below 0.6 keV becomes incoherent with the power-law and
higher-energy disc emission at frequencies below 0.5 Hz, in contrast with the
coherent variations seen in the 2006 data.
We explain these differences and the associated complex lags in the 2009 data
in terms of the fluctuating disc model. If the variable signals are generated
at small radii in the disc, the variability of disc emission can be naturally
suppressed by the fraction of unmodulated disc emission from larger radii. The
drop in coherence can be produced by disc accretion fluctuations arising at
larger radii which are viscously damped and hence unable to propagate to the
inner, power-law emitting region.Comment: 15 pages, 11 figures. Accepted for publication in MNRA
The 'Corona Verde' Strategic Plan: an integrated vision for protecting and enhancing the natural and cultural heritage
The ‘Corona Verde' [Green Crown] Strategic Plan is a net of ecological corridors, greenways, rural areas and UNESCO Sites, including all the open spaces in the metropolitan area of Turin (Italy). Its main goal is to link together policies for nature, landscape and cultural heritage, creating a new and alternative vision of the territory, based on the quality of the environment and of life. Since 2000, when the project started, more than €23 million have been invested by the European Union and the Piedmont Region, and, now, the first results can be analysed. Corona Verde introduces innovative approaches to environmental and urban strategies and in governance processes
The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A
The presence of narrow high-temperature emission lines from nitrogen-rich gas
close to SN 1987A has been the principal observational constraint on the evolu-
tionary status of the supernova's progenitor. A new analysis of the complete
five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A
(1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII]
1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and
systematic errors and reveals significant short-term fluctuations in the light
curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days
and show a progression from high to low ionization potential, implying an ioni-
zation gradient in the emitting region. The line emission turns on suddenly at
83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches
peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and
inclination of 41.0+/-3.9 is derived from these times, assuming a circular
ring. The probable role of resonant scattering in the N V light curve
introduces systematic errors that leads us to exclude this line from the timing
analysis. A new nebular analysis yields improved CNO abundance ratios
N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in
our previous paper. From the late-time behavior of the light curves we find
that the emission origi- nates from progressively lower density gas. We
estimate the emitting mass near maximum (roughly 400 days) to be roughly
4.7E{-2} solar masses, assuming a filling factor of unity and an electron
density of 2.6E4 cm^{-3}. These results are discussed in the context of current
models for the emission and hydrodynamics of the ring.Comment: 38 pages, AASTeX v.4.0, 13 Postscript figures; ApJ, in pres
The C IV Doublet Ratio Intensity Effect in Symbiotic Stars
The first successful high-resolution ultraviolet spectra in the λλ 1200-2000 wavelength range of the symbiotic variable R Aquarii and its nebular Jet were obtained in 1987 July with the International Ultraviolet Explorer (IUE). The line profile structure of the C IV λλ1548, 1550 doublet in the jet indicates multicomponent velocity structure from an optically thin emitting gas. The C IV doublet profiles in the compact H II region engulfing the Mira and hot companion binary also suggest multicomponent structure, in which the radial velocities range up to ~ -100 km s^- 1. The value of the doublet intensity ratio in the R Aqr H II region is I(λ1548)/ I(λ1550) ~0.6, which is less than the optically thick limit of unity, an effect which has also been observed in other similar symbiotic stars such as RX Pup. In the case of RX Pup, however, the C IV doublet intensity ratio was I(λ1548)/I(λ1550) ~0.6 during an enhanced phase of UV and optical emission, but became larger, acquiring a value ~1, as the star declined in light over a 5 yr period. The anomalous behavior of the C IV doublet intensities, which. we refer to as the C IV Doublet Ratio Intensity Effect, may provide an important tool for studying the spatial structure and temporal nature of winds in symbiotic stars
Joint spectral-timing modelling of the hard lags in GX 339-4: constraints on reflection models
The X-ray variations of hard state black hole X-ray binaries above 2 keV show
'hard lags', in that the variations at harder energies follow variations at
softer energies, with a time-lag \tau depending on frequency \nu approximately
as \tau \propto \nu^{-0.7}. Several models have so far been proposed to explain
this time delay, including fluctuations propagating through an accretion flow,
spectral variations during coronal flares, Comptonisation in the extended hot
corona or a jet, or time-delays due to large-scale reflection from the
accretion disc. In principle these models can be used to predict the shape of
the energy spectrum as well as the frequency-dependence of the time-lags,
through the construction of energy-dependent response functions which map the
emission as a function of time-delay in the system. Here we use this approach
to test a simple reflection model for the frequency-dependent lags seen in the
hard state of GX 339-4, by simultaneously fitting the model to the
frequency-dependent lags and energy spectrum measured by XMM-Newton in 2004 and
2009. Our model cannot simultaneously fit both the lag and spectral data, since
the relatively large lags require an extremely flared disc which subtends a
large solid angle to the continuum at large radii, in disagreement with the
observed Fe K\alpha emission. Therefore, we consider it more likely that the
lags > 2 keV are caused by propagation effects in the accretion flow, possibly
related to the accretion disc fluctuations which have been observed previously.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
Mg II h + k emission lines as stellar activity indicators of main sequence F-K stars
The main purpose of this study is to use the IUE spectra in the analysis of
magnetic activity of main sequence F-K stars. Combining IUE observations of
MgII and optical spectroscopy of Ca II, the registry of ctivity of stars can be
extended in time. We retrieved all the high-resolution spectra of F, G, and K
main sequence stars observed by IUE (i.e. 1623 spectra of 259 F to K dwarf
stars). We obtained the continuum surface flux near the Mg II h+k lines near
2800 \AA and the MgII line-core surface flux from the IUE spectra. We obtained
a relation between the mean continuum flux near the MgII lines with the colour
of the star. For a set of 117 nearly simultaneous observations of Mg II
and Ca II fluxes of 21 F5 to K3 main sequence stars, we obtained a colour
dependent relation between the Mount Wilson CaII S-index and the MgII emission
line-core flux. As an application of this calibration, we computed the Mount
Wilson index for all the dF to dK stars which have high resolution IUE spectra.
For some of the most frequently observed main sequence stars, we analysed the
Mount Wilson index S from the IUE spectra, together with the ones derived from
visible spectra. We confirm the cyclic chromospheric activity of epsilon Eri
(HD 22049) and beta Hydri (HD 2151), and we find a magnetic cycle in alpha Cen
B (HD 128621). Complete abstract in the paper.Comment: 10 pages, accepted for publication in Astronomy and Astrophysic
Tumour-infiltrating lymphocytes bear the 75 kDa tumour necrosis factor receptor.
Tumour necrosis factor alpha (TNF-alpha) is a cytokine with a variety of immunological properties. The identification of two receptors for this molecule, i.e. the 75 kDa and the 55 kDa TNF receptors (TNF-R), recently clarified the mechanisms through which this cytokine provides its wide range of immunomodulatory activities. In this study we have investigated the expression and the functional properties of these receptors on tumour-infiltrating lymphocytes (TILs) recovered from 17 patients with solid cancers (melanoma, colorectal carcinoma and lung cancer). To this end, TIL lines and freshly isolated TILs were evaluated for (a) the expression and the functional role of TNF receptors following culture in the presence of interleukin 2 (IL-2) and (b) the production of TNF-alpha following culture with IL-2 and the role of this cytokine in IL-2-driven TIL proliferation. Flow cytometry analysis demonstrated that TILs bear the 75 kDa TNF-R. Moreover, TIL lines express detectable messages for TNF-alpha and release this cytokine. Functional in vitro studies have shown that anti-TNF-alpha, as well as anti-75 kDa TNF-R antibodies, are able to inhibit the IL-2-induced TIL proliferation. These data demonstrate that TILs are equipped with a fully functional TNF-R system and suggest a putative role for this receptor and its ligand in the activation and expression of TILs following immunotherapy with IL-2
X-ray and UV observations of nova V598 Puppis between 147 and 255 days after outburst
Aims: The launch of Swift has allowed many more novae to be observed
regularly over the X-ray band. Such X-ray observations of novae can reveal
ejecta shocks and the nuclear burning white dwarf, allowing estimates to be
made of the ejecta velocity. Methods: We analyse XMM-Newton and Swift X-ray and
UV observations of the nova V598 Pup, which was initially discovered in the
XMM-Newton slew survey. These data were obtained between 147 and 255 days after
the nova outburst, and are compared with the earlier, brighter slew detection.
Results: The X-ray spectrum consists of a super-soft source, with the soft
emission becoming hotter and much fainter between days ~147 and ~172 after the
outburst, and a more slowly declining optically thin component, formed by
shocks with kT ~ 200-800 eV (corresponding to velocities of 400-800 km s^-1).
The main super-soft phase had a duration of less than 130 days. The Reflection
Grating Spectrometer data show evidence of emission lines consistent with
optically thin emission of kT ~100 eV and place a limit on the density of the
surrounding medium of log(n_e/cm^-3) < 10.4 at the 90 % level. The UV emission
is variable over short timescales and fades by at least one magnitude (at
lambda ~ 2246-2600 angstrom) between days 169 and 255.Comment: 6 pages, 5 figures, accepted for publication in A&
Modeling of the Super-Eddington Phase for Classical Novae: Five IUE Novae
We present a light curve model for the super-Eddington luminosity phase of
five classical novae observed with IUE. Optical and UV light curves are
calculated based on the optically thick wind theory with a reduced effective
opacity for a porous atmosphere. Fitting a model light curve with the UV 1455
\AA light curve, we determine the white dwarf mass and distance to be (1.3
M_sun, 4.4 kpc) for V693 CrA, (1.05 M_sun, 1.8 kpc) for V1974 Cyg, (0.95 M_sun,
4.1 kpc) for V1668 Cyg, (1.0 M_sun, 2.1 kpc) for V351 Pup, and (1.0 M_sun, 4.3
kpc) for OS And.Comment: 9 pages including 8 figures, to appear in the Astrophysical Journa
Cyclin-dependent kinases 7 and 9 specifically regulate neutrophil transcription and their inhibition drives apoptosis to promote resolution of inflammation
Terminally differentiated neutrophils are short-lived but the key effector cells of the innate immune response, and have a prominent role in the pathogenesis and propagation of many inflammatory diseases. Delayed apoptosis, which is responsible for their extended longevity, is critically dependent on a balance of intracellular survival versus pro-apoptotic proteins. Here, we elucidate the mechanism by which the cyclin-dependent kinase (CDK) inhibitor drugs such as R-roscovitine and DRB (5,6-dichloro-1-beta--ribofuranosylbenzimidazole) mediate neutrophil apoptosis. We demonstrate (by a combination of microarray, confocal microscopy, apoptosis assays and western blotting) that the phosphorylation of RNA polymerase II by CDKs 7 and 9 is inhibited by R-roscovitine and that specific effects on neutrophil transcriptional capacity are responsible for neutrophil apoptosis. Finally, we show that specific CDK7 and 9 inhibition with DRB drives resolution of neutrophil-dominant inflammation. Thus, we highlight a novel mechanism that controls both primary human neutrophil transcription and apoptosis that could be targeted by selective CDK inhibitor drugs to resolve established inflammation
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