2,451 research outputs found
A new super-soft X-ray source in the Small Magellanic Cloud: Discovery of the first Be/white dwarf system in the SMC?
The Small Magellanic Cloud (SMC) hosts a large number of Be/X-ray binaries,
however no Be/white dwarf system is known so far, although population synthesis
calculations predict that they might be more frequent than Be/neutron star
systems. XMMUJ010147.5-715550 was found as a new faint super-soft X-ray source
(SSS) with a likely Be star optical counterpart. We investigate the nature of
this system and search for further high-absorbed candidates in the SMC. We
analysed the XMM-Newton X-ray spectrum and light curve, optical photometry, and
the I-band OGLE III light curve. The X-ray spectrum is well represented by
black-body and white dwarf atmosphere models with highly model-dependent
temperature between 20 and 100 eV. The likely optical counterpart AzV 281
showed low near infrared emission during X-ray activity, followed by a
brightening in the I-band afterwards. We find further candidates for
high-absorbed SSSs with a blue star as counterpart. We discuss
XMMUJ010147.5-715550 as the first candidate for a Be/white dwarf binary system
in the SMC.Comment: 6 pages, 4 figures, accepted by A&
Persistent detwinning of iron pnictides by small magnetic fields
Our comprehensive study on EuFeAs reveals a dramatic reduction of
magnetic detwinning fields compared to other AFeAs (A = Ba, Sr, Ca)
iron pnictides by indirect magneto-elastic coupling of the Eu ions. We
find that only 0.1T are sufficient for persistent detwinning below the local
Eu ordering; above = 19K, higher fields are necessary.
Even after the field is switched off, a significant imbalance of twin domains
remains constant up to the structural and electronic phase transition (190K).
This persistent detwinning provides the unique possibility to study the low
temperature electronic in-plane anisotropy of iron pnictides without applying
any symmetrybreaking external force.Comment: accepted by Physical Review Letter
The XMM-Newton survey of the Small Magellanic Cloud: The X-ray point-source catalogue
Local-Group galaxies provide access to samples of X-ray source populations of
whole galaxies. The XMM-Newton survey of the Small Magellanic Cloud (SMC)
completely covers the bar and eastern wing with a 5.6 deg^2 area in the
(0.2-12.0) keV band. To characterise the X-ray sources in the SMC field, we
created a catalogue of point sources and sources with moderate extent. Sources
with high extent (>40") have been presented in a companion paper. We searched
for point sources in the EPIC images using sliding-box and maximum-likelihood
techniques and classified the sources using hardness ratios, X-ray variability,
and their multi-wavelength properties. The catalogue comprises 3053 unique
X-ray sources with a median position uncertainty of 1.3" down to a flux limit
for point sources of ~10^-14 erg cm^-2 s^-1 in the (0.2-4.5) keV band,
corresponding to 5x10^33 erg s^-1 for sources in the SMC. We discuss
statistical properties, like the spatial distribution, X-ray colour diagrams,
luminosity functions, and time variability. We identified 49 SMC high-mass
X-ray binaries (HMXB), four super-soft X-ray sources (SSS), 34 foreground
stars, and 72 active galactic nuclei (AGN) behind the SMC. In addition, we
found candidates for SMC HMXBs (45) and faint SSSs (8) as well as AGN (2092)
and galaxy clusters (13). We present the most up-to-date catalogue of the X-ray
source population in the SMC field. In particular, the known population of
X-ray binaries is greatly increased. We find that the bright-end slope of the
luminosity function of Be/X-ray binaries significantly deviates from the
expected universal high-mass X-ray binary luminosity function.Comment: 32 pages, 18 figures, accepted for publication in A&A, catalog will
be available at CD
Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers
Magnetic properties of thin (Ga,Mn)As layers improve during annealing by
out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms
participate in the growth of a Mn-rich surface layer and a saturation of this
layer causes an inhibition of the out-diffusion. We combine high-resolution
x-ray diffraction with x-ray absorption spectroscopy and a numerical solution
of the diffusion problem for the study of the out-diffusion of Mn interstitials
during a sequence of annealing steps. Our data demonstrate that the
out-diffusion of the interstitials is substantially affected by the internal
electric field caused by an inhomogeneous distribution of charges in the
(Ga,Mn)As layer.Comment: 11 pages, 5 figure
AGN behind the SMC selected from radio and X-ray surveys
The XMM-Newton survey of the Small Magellanic Cloud (SMC) revealed 3053 X-ray
sources with the majority expected to be active galactic nuclei (AGN) behind
the SMC. However, the high stellar density in this field often does not allow
assigning unique optical counterparts and hinders source classification. On the
other hand, the association of X-ray point sources with radio emission can be
used to select background AGN with high confidence, and to constrain other
object classes like pulsar wind nebula. To classify X-ray and radio sources, we
use clear correlations of X-ray sources found in the XMM-Newton survey with
radio-continuum sources detected with ATCA and MOST. Deep radio-continuum
images were searched for correlations with X-ray sources of the XMM-Newton
SMC-survey point-source catalogue as well as galaxy clusters seen with extended
X-ray emission. Eighty eight discrete radio sources were found in common with
the X-ray point-source catalogue in addition to six correlations with extended
X-ray sources. One source is identified as a Galactic star and eight as
galaxies. Eight radio sources likely originate in AGN that are associated with
clusters of galaxies seen in X-rays. One source is a PWN candidate. We obtain
43 new candidates for background sources located behind the SMC. A total of 24
X-ray sources show jet-like radio structures.Comment: 9 pages, 6 figures, accepted for publication in A&
A 100ks XMM-Newton view of the Seyfert 1.8 ESO113-G010. I. Discovery of large X-ray variability and study of the FeKalpha line complex
(Abridged) We present here a long (100ks) XMM-Newton follow-up of the Seyfert
1.8 galaxy ESO113-G010 performed in November 2005, in order to study over a
longer time-scale its main X-ray properties. The source was found in a
higher/softer time-averaged flux state, and timing analysis of this source
reveals strong, rapid variability. The Power Spectral Density (PSD) analysis
indicates (at 95% c.l.) a break at 3.7 x 10^-4 Hz. This cut-off frequency is
comparable to those measured in some other rapidly-variable Seyferts, such as
MCG-6-30-15 and NGC4051. From the mass-luminosity-time-scale, we infer that
M_BH ranges from 4 x 10^6 - 10^7 M_odot and the source is accreting at or close
to the Eddington rate (or even higher). The existing data cannot distinguish
between spectral pivoting of the continuum and a two-component origin for the
spectral softening, primarily because the data do not span a broad enough flux
range. In the case of the two-component model, the fractional offsets measured
in the flux-flux plots increase significantly toward higher energies (similar
to what is observed in MCG-6-30-15) as expected if there exists a constant
reflection component. Contrary to May 2001, no significant highly redshifted
emission line is observed (which might be related to the source flux level),
while two narrow emission lines at about 6.5keV and 7keV are observed. The S/N
is not high enough to establish if the lines are variable or constant. As
already suggested by the 2001 observation, no significant constant narrow
6.4keV FeK line (EW~32eV) is observed, hence excluding any dominant emission
from distant cold matter such as a torus in this Seyfert type 1.8 galaxy.Comment: Accepted for publication in A&A, 10 pages, 11 figures, 2 table
Step by step capping and strain state of GaN/AlN quantum dots studied by grazing incidence diffraction anomalous fine structure
The investigation of small size embedded nanostructures, by a combination of
complementary anomalous diffraction techniques, is reported. GaN Quantum Dots
(QDs), grown by molecular beam epitaxy in a modified Stranski-Krastanow mode,
are studied in terms of strain and local environment, as a function of the AlN
cap layer thickness, by means of grazing incidence anomalous diffraction. That
is, the X-ray photons energy is tuned across the Ga absorption K-edge which
makes diffraction chemically selective. Measurement of \textit{hkl}-scans,
close to the AlN (30-30) Bragg reflection, at several energies across the Ga
K-edge, allows the extraction of the Ga partial structure factor, from which
the in-plane strain of GaN QDs is deduced. From the fixed-Q energy-dependent
diffracted intensity spectra, measured for diffraction-selected iso-strain
regions corresponding to the average in-plane strain state of the QDs,
quantitative information regarding composition and the out-of-plane strain has
been obtained. We recover the in-plane and out-of-plane strains in the dots.
The comparison to the biaxial elastic strain in a pseudomorphic layer indicates
a tendency to an over-strained regime.Comment: submitted to PR
Taking Differences in Institutional Quality into Account in Global Forest Modelling
Forest cover and land-use change models are commonly used for climate scenarios and provide policy advice. The IIASA Global Forest Model (G4M) compares the net present value of agriculture and forestry, and makes a land-use change decision, based on this comparison.
Moving beyond this purely economic rationale, we aimed at understanding in how far integrating differences in environmental institutional quality, could allow improving the representation of forest cover change processes of the model. Through an econometric regression analysis, we identified the most significant out of a larger set of variables on environmental institutional quality and created a composite index. We then implemented the composite index into the model. Its components are: the internalization of environmental norms, the strength of institutions, the ability of the institutions to guarantee macroeconomic stability, the quality of the administration and the efficiency of the bureaucracy.
Through the inclusion of the composite index, the model’s residual could be significantly reduced. The results suggest that future research should consider taking differences in environmental institutional quality into account to improve modeling of deforestation processes. Moreover, the implementation of the index into the model allows for the first time to create scenarios for institutional quality and its impact on forest cover
Bipolar-Hyper-Shell Galactic Center Statrburst Model: Further Evidence from ROSAT Data and New Radio and X-ray Simulations
Using the all-sky ROSAT soft X-ray and 408-MHz radio continuum data, we show
that the North Polar Spur and its western and southern counter-spurs draw a
giant dumbbell-shape necked at the galactic plane. We interpret these features
as due to a shock front originating from a starburst 15 million years ago with
a total energy of the order of ergs or type II
supernovae. We simulate all-sky distributions of radio continuum and soft X-ray
intensities based on the bipolar-hyper-shell galactic center starburst model.
The simulations can well reproduce the radio NPS and related spurs, as well as
radio spurs in the tangential directions of spiral arms. Simulated X-ray maps
in 0.25, 0.75 and 1.5 keV bands reproduce the ROSAT X-ray NPS, its western and
southern counter-spurs, and the absorption layer along the galactic plane. We
propose to use the ROSAT all-sky maps to probe the physics of gas in the
halo-intergalactic interface, and to directly date and measure the energy of a
recent Galactic Center starburst.Comment: To appear in ApJ, Latex MS in ApJ macro, 8 figures in jpg (original
quality ps figs available on request
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