1,228 research outputs found
The X-ray nebula of the filled center supernova remnant 3C58 and its interaction with the environment
An \xmm observation of the plerionic supernova remnant 3C58 has allowed us to
study the X-ray nebula with unprecedented detail. A spatially resolved spectral
analysis with a resolution of 8\arcsec has yielded a precise determination of
the relation between the spectral index and the distance from the center. We do
not see any evidence for bright thermal emission from the central core. In
contrast with previous ASCA and {\em Einstein} results, we derive an upper
limit to the black-body 0.5-10 keV luminosity and emitting area of \ergsec and cm, respectively, ruling out
emission from the hot surface of the putative neutron star and also excluding
the "outer-gap" model for hot polar caps. We have performed for the first time
a spectral analysis of the outer regions of the X-ray nebula, where most of the
emission is still non-thermal, but where the addition of a soft (kT=0.2-0.3
keV) optically thin plasma component is required to fit the spectrum at
keV. This component provides 6% of the whole remnant observed flux in the
0.5-10.0 keV band. We show that a Sedov interpretation is incompatible with the
SN1181-3C58 association, unless there is a strong deviation from electron-ion
energy equipartition, and that an origin of this thermal emission in terms of
the expansion of the nebula into the ejecta core nicely fits all the radio and
X-ray observations.Comment: 10 pages, 7 figures, accepted for publication in A&
UV observations of the galaxy cluster Abell 1795 with the optical monitor on XMM-Newton
We present the results of an analysis of broad band UV observations of the
central regions of Abell 1795 observed with the optical monitor on XMM-Newton.
As have been found with other UV observations of the central regions of
clusters of galaxies, we find evidence for star formation. However, we also
find evidence for absorption in the cD galaxy on a more extended scale than has
been seen with optical imaging. We also report the first UV observation of part
of the filamentary structure seen in H, X-rays and very deep U band
imaging. The part of the filament we see is very blue with UV colours
consistent with a very early (O/B) stellar population. This is the first direct
evidence of a dominant population of early type stars at the centre of Abell
1795 and implies very recent star formation at the centre of this clusterComment: 6 pages, 3 figures accepted by A&A Letter
X-ray Spectroscopy of the Cluster of Galaxies Abell 1795 with XMM-Newton
The initial results from XMM-Newton observations of the rich cluster of
galaxies Abell 1795 are presented. The spatially-resolved X-ray spectra taken
by the European Photon Imaging Cameras (EPIC) show a temperature drop at a
radius of kpc from the cluster center, indicating that the ICM is
cooling. Both the EPIC and the Reflection Grating Spectrometers (RGS) spectra
extracted from the cluster center can be described by an isothermal model with
a temperature of keV. The volume emission measure of any cool
component ( keV) is less than a few % of the hot component at the cluster
center. A strong OVIII Lyman-alpha line was detected with the RGS from the
cluster core. The O abundance and its ratio to Fe at the cluster center is
0.2--0.5 and 0.5--1.5 times the solar value, respectively.Comment: Accepted: A&A Letters, 2001, 6 page
Constraining the thermal history of the Warm-Hot Intergalactic Medium
We have identified a large-scale structure traced by galaxies at z=0.8,
within the Lockman Hole, by means of multi-object spectroscopic observations.
By using deep XMM images we have investigated the soft X-ray emission from the
Warm-Hot Intergalactic Medium (WHIM) expected to be associated with this
large-scale structure and we set a tight upper limit to its flux in the very
soft 0.2-0.4 keV band. The non-detection requires the WHIM at these redshifts
to be cooler than 0.1 keV. Combined with the WHIM emission detections at lower
redshift, our result indicates that the WHIM temperature is rapidly decreasing
with redshift, as expected in popular cosmological models.Comment: 10 pages, 5 figures, 1 appendix. A&A accepte
Construction and commissioning of a technological prototype of a high-granularity semi-digital hadronic calorimeter
A large prototype of 1.3m3 was designed and built as a demonstrator of the
semi-digital hadronic calorimeter (SDHCAL) concept proposed for the future ILC
experiments. The prototype is a sampling hadronic calorimeter of 48 units. Each
unit is built of an active layer made of 1m2 Glass Resistive Plate
Chamber(GRPC) detector placed inside a cassette whose walls are made of
stainless steel. The cassette contains also the electronics used to read out
the GRPC detector. The lateral granularity of the active layer is provided by
the electronics pick-up pads of 1cm2 each. The cassettes are inserted into a
self-supporting mechanical structure built also of stainless steel plates
which, with the cassettes walls, play the role of the absorber. The prototype
was designed to be very compact and important efforts were made to minimize the
number of services cables to optimize the efficiency of the Particle Flow
Algorithm techniques to be used in the future ILC experiments. The different
components of the SDHCAL prototype were studied individually and strict
criteria were applied for the final selection of these components. Basic
calibration procedures were performed after the prototype assembling. The
prototype is the first of a series of new-generation detectors equipped with a
power-pulsing mode intended to reduce the power consumption of this highly
granular detector. A dedicated acquisition system was developed to deal with
the output of more than 440000 electronics channels in both trigger and
triggerless modes. After its completion in 2011, the prototype was commissioned
using cosmic rays and particles beams at CERN.Comment: 49 pages, 41 figure
XMM-Newton observation of the Lockman Hole; I. The X-ray Data
We report on the first deep X-ray survey with the XMM-Newton observatory
during the performance verification phase. The field of the Lockman Hole, one
of the best studied sky areas over a very wide range of wavelengths, has been
observed. A total of ~100 ksec good exposure time has been accumulated.
Combining the images of the European Photon Imaging Camera (EPIC) detectors we
reach a flux limit of 0.31, 1.4 and 2.4 X 10^{-15} erg cm^{-2} s^{-1},
respectively in the 0.5-2, 2-10, and 5-10 keV band. Within an off-axis angle of
10 arcmin we detect 148, 112 and 61 sources, respectively. The log(N)-log(S)
relation in the three bands is compared with previous results. In particular in
the 5-10 keV band these observations present the deepest X-ray survey ever,
about a factor 20 more sensitive than the previous BeppoSAX observations. Using
X-ray spectral diagnostics and the set of previously known, spectroscopically
identified ROSAT sources in the field, the new sources can be classified.
XMM-Newton detects a significant number (~40%) of X-ray sources with hard,
probably intrinsically absorbed X-ray spectra, confirming a prediction of the
population synthesis models for the X-ray background.Comment: 6 pages, based on the new A&A style file (included), to be published
in A&A 365 (2001, special XMM issue), one page contains color image
Tracing cosmic evolution with clusters of galaxies
The most successful cosmological models to date envision structure formation
as a hierarchical process in which gravity is constantly drawing lumps of
matter together to form increasingly larger structures. Clusters of galaxies
currently sit atop this hierarchy as the largest objects that have had time to
collapse under the influence of their own gravity. Thus, their appearance on
the cosmic scene is also relatively recent. Two features of clusters make them
uniquely useful tracers of cosmic evolution. First, clusters are the biggest
things whose masses we can reliably measure because they are the largest
objects to have undergone gravitational relaxation and entered into virial
equilibrium. Mass measurements of nearby clusters can therefore be used to
determine the amount of structure in the universe on scales of 10^14 to 10^15
solar masses, and comparisons of the present-day cluster mass distribution with
the mass distribution at earlier times can be used to measure the rate of
structure formation, placing important constraints on cosmological models.
Second, clusters are essentially ``closed boxes'' that retain all their gaseous
matter, despite the enormous energy input associated with supernovae and active
galactic nuclei, because the gravitational potential wells of clusters are so
deep. The baryonic component of clusters therefore contains a wealth of
information about the processes associated with galaxy formation, including the
efficiency with which baryons are converted into stars and the effects of the
resulting feedback processes on galaxy formation. This article reviews our
theoretical understanding of both the dark-matter component and the baryonic
component of clusters. (Abridged)Comment: 54 pages, 15 figures, Rev. Mod. Phys. (in press
Performance of Glass Resistive Plate Chambers for a high granularity semi-digital calorimeter
A new design of highly granular hadronic calorimeter using Glass Resistive
Plate Chambers (GRPCs) with embedded electronics has been proposed for the
future International Linear Collider (ILC) experiments. It features a 2-bit
threshold semi-digital read-out. Several GRPC prototypes with their electronics
have been successfully built and tested in pion beams. The design of these
detectors is presented along with the test results on efficiency, pad
multiplicity, stability and reproducibility.Comment: 16 pages, 15 figure
Recommendations for the medical evaluation of children prior to adoption in South Africa
The current legislative framework in South Africa (SA) supports adoption as the preferred form of care for children with inadequate or no parental or family support. There are an estimated 3.8 million orphans in SA, with approximately 1.5 - 2 million children considered adoptable. As a means of improving services, newly drafted adoption guidelines from the National Department of Social Development will in future require both non-profit and private sector adoption agencies to obtain a medical report on a child prior to placement. However, no local guidelines specify what an appropriate medical examination entails or how it should be reported. For the purposes of proposing and developing such guidelines, an open forum was convened at the Institute of Pathology, University of Pretoria, in March 2013. These ‘Recommendations for the medical evaluation of children prior to adoption in South Africa’ emanate from this meeting
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