4,513 research outputs found
XMM-Newton observations of SNR 1987A. II. The still increasing X-ray light curve and the properties of Fe K lines
Aims. We report on the recent observations of the supernova remnant SNR 1987A
in the Large Magellanic Cloud with XMM-Newton. Carefully monitoring the
evolution of the X-ray light curve allows to probe the complex circumstellar
medium structure observed around the supernova progenitor star.
Methods. We analyse all XMM-Newton observations of SNR 1987A from January
2007 to December 2011, using data from the EPIC-pn camera. Spectra from all
epochs are extracted and analysed in a homogeneous way. Using a multi-shock
model to fit the spectra across the 0.2-10 keV band we measure soft and hard
X-ray fluxes with high accuracy. In the hard X-ray band we examine the presence
and properties of Fe K ines. Our findings are interpreted in the framework of a
hydrodynamics-based model.
Results. The soft X-ray flux of SNR 1987A continuously increased in the
recent years. Although the light curve shows a mild flattening, there is no
sudden break as reported in an earlier work, a picture echoed by a revision of
the Chandra light curve. We therefore conclude that material in the equatorial
ring and out-of-plane HII regions are still being swept-up. We estimate the
thickness of the equatorial ring to be at least 4.5x10^16 cm (0.0146 pc). This
lower limit will increase as long as the soft X-ray flux has not reached a
turn-over. We detect a broad Fe K line in all spectra from 2007 to 2011. The
widths and centroid energies of the lines indicate the presence of a collection
of iron ionisation stages. Thermal emission from the hydrodynamic model does
not reproduce the low-energy part of the line (6.4-6.5 keV), suggesting that
fluorescence from neutral and/or low ionisation Fe might be present.Comment: 4 pages, 3 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysic
Nanometer-scale Tomographic Reconstruction of 3D Electrostatic Potentials in GaAs/AlGaAs Core-Shell Nanowires
We report on the development of Electron Holographic Tomography towards a
versatile potential measurement technique, overcoming several limitations, such
as a limited tilt range, previously hampering a reproducible and accurate
electrostatic potential reconstruction in three dimensions. Most notably,
tomographic reconstruction is performed on optimally sampled polar grids taking
into account symmetry and other spatial constraints of the nanostructure.
Furthermore, holographic tilt series acquisition and alignment have been
automated and adapted to three dimensions. We demonstrate 6 nm spatial and 0.2
V signal resolution by reconstructing various, previously hidden, potential
details of a GaAs/AlGaAs core-shell nanowire. The improved tomographic
reconstruction opens pathways towards the detection of minute potentials in
nanostructures and an increase in speed and accuracy in related techniques such
as X-ray tomography
Development of a methodology for studying tunnel climate in long railway tunnels and for optimizing the design process of cross-passage cooling systems
When it comes into operation in 2026, the Koralmtunnel in Austria will be the world́s seventh longest railway
tunnel. The installation of the power supply, telecommunications and electro-mechanical services is currently
ongoing. Parts of these systems have to be protected from temperature and humidity variations and from the high
dust loads which are characteristic of the tunnel atmosphere. In particular, cooling systems are required to
counteract the significant amounts of heat released by some installations. Information on a large number of
parameters (e.g. tunnel air temperatures) is required in the design process. However, such information is only
partly available in the design stage. Hence, a prediction of tunnel air temperatures has to be made. Additionally,
since hardly any information about the tunnel climate in long railway tunnels is available and in-situ mea-
surements are not possible, as thermal conditions differ significantly between the construction/equipping phase
and the operation phase, a novel methodology for the prediction of the tunnel climate had to be developed. This
article presents a description of a new method comprising four main investigative steps and of its application to
the Koralmtunnel as a selected case study. While steps 1 and 2 provide information about the actual cooling
requirement and tunnel air temperatures for a period of 50 years, steps three and four of the investigation aim at
the technical and economic optimization of cooling systems
Searching for molecular outflows in Hyper-Luminous Infrared Galaxies
We present constraints on the molecular outflows in a sample of five
Hyper-Luminous Infrared Galaxies using Herschel observations of the OH doublet
at 119 {\mu}m. We have detected the OH doublet in three cases: one purely in
emission and two purely in absorption. The observed emission profile has a
significant blueshifted wing suggesting the possibility of tracing an outflow.
Out of the two absorption profiles, one seems to be consistent with the
systemic velocity while the other clearly indicates the presence of a molecular
outflow whose maximum velocity is about ~1500 km/s. Our analysis shows that
this system is in general agreement with previous results on Ultra-luminous
Infrared Galaxies and QSOs, whose outflow velocities do not seem to correlate
with stellar masses or starburst luminosities (star formation rates). Instead
the galaxy outflow likely arises from an embedded AGN.Comment: Accepted for publication in MNRAS. 13 pages, 11 figures, 4 table
Imaging density disturbances in water with 41.3 attosecond time resolution
We show that the momentum flexibility of inelastic x-ray scattering may be
exploited to invert its loss function, alowing real time imaging of density
disturbances in a medium. We show the disturbance arising from a point source
in liquid water, with a resolution of 41.3 attoseconds (
sec) and 1.27 ( cm). This result is used to
determine the structure of the electron cloud around a photoexcited molecule in
solution, as well as the wake generated in water by a 9 MeV gold ion. We draw
an analogy with pump-probe techniques and suggest that energy-loss scattering
may be applied more generally to the study of attosecond phenomena.Comment: 4 pages, 4 color figure
On the Nodal Count Statistics for Separable Systems in any Dimension
We consider the statistics of the number of nodal domains aka nodal counts
for eigenfunctions of separable wave equations in arbitrary dimension. We give
an explicit expression for the limiting distribution of normalised nodal counts
and analyse some of its universal properties. Our results are illustrated by
detailed discussion of simple examples and numerical nodal count distributions.Comment: 21 pages, 4 figure
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Evaluation of peak-picking algorithms for protein mass spectrometry
Peak picking is an early key step in MS data analysis. We compare three commonly used approaches to peak picking and discuss their merits by means of statistical analysis. Methods investigated encompass signal-to-noise ratio, continuous wavelet transform, and a correlation-based approach using a Gaussian template.
Functionality of the three methods is illustrated and discussed in a practical context using a mass spectral data set created with MALDI-TOF technology. Sensitivity and specificity are investigated using a manually defined reference set of peaks. As an additional criterion, the robustness of the three methods is assessed by a perturbation analysis and illustrated using ROC curves
High-ionization mid-infrared lines as black hole mass and bolometric luminosity indicators in active galactic nuclei
We present relations of the black hole mass and the optical luminosity with
the velocity dispersion and the luminosity of the [Ne V] and the [O IV]
high-ionization lines in the mid-infrared (MIR) for 28 reverberation-mapped
active galactic nuclei. We used high-resolution Spitzer Infrared Spectrograph
and Infrared Space Observatory Short Wavelength Spectrometer data to fit the
profiles of these MIR emission lines that originate from the narrow-line region
of the nucleus. We find that the lines are often resolved and that the velocity
dispersion of [Ne V] and [O IV] follows a relation similar to that between the
black hole mass and the bulge stellar velocity dispersion found for local
galaxies. The luminosity of the [Ne V] and the [O IV] lines in these sources is
correlated with that of the optical 5100A continuum and with the black hole
mass. Our results provide a means to derive black hole properties in various
types of active galactic nuclei, including highly obscured systems.Comment: accepted for publication in ApJ
An infrared study of the double nucleus in NGC3256
We present new resolved near and mid-IR imaging and N-band spectroscopy of
the two nuclei in the merger system NGCA3256, the most IR luminous galaxy in
the nearby universe. The results from the SED fit to the data are consistent
with previous estimates of the amount of obscuration towards the nuclei and the
nuclear star formation rates. However, we also find substantial differences in
the infrared emission from the two nuclei which cannot be explained by
obscuration alone. We conclude that the northern nucleus requires an additional
component of warm dust in order to explain its properties. This suggests that
local starforming conditions can vary significantly within the environment of a
single system.Comment: Accepted for publication (MNRAS
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