735 research outputs found
Absolute kinematics of radio source components in the complete S5 polar cap sample. III. First wide-field high-precision astrometry at 15.4 GHz
We report on the first wide-field, high-precision astrometric analysis of the
13 extragalactic radio sources of the complete S5 polar cap sample at 15.4 GHz.
We describe new algorithms developed to enable the use of differenced phase
delays in wide-field astrometric observations and discuss the impact of using
differenced phase delays on the precision of the wide-field astrometric
analysis. From this global fit, we obtained estimates of the relative source
positions with precisions ranging from 14 to 200 as at 15.4 GHz, depending
on the angular separation of the sources (from 1.6 to 20.8
degrees). These precisions are 10 times higher than the achievable
precisions using the phase-reference mapping technique.Comment: 9 pages, 7 figure
On the coherence loss in phase-referenced VLBI observations
Context: Phase referencing is a standard calibration technique in radio
interferometry, particularly suited for the detection of weak sources close to
the sensitivity limits of the interferometers. However, effects from a changing
atmosphere and inaccuracies in the correlator model may affect the
phase-referenced images, leading to wrong estimates of source flux densities
and positions. A systematic observational study of signal decoherence in phase
referencing, and its effects in the image plane, has not been performed yet.
Aims: We systematically studied how the signal coherence in
Very-Long-Baseline-Interferometry (VLBI) observations is affected by a
phase-reference calibration at different frequencies and for different
calibrator-to-target separations. The results obtained should be of interest
for a correct interpretation of many phase-referenced observations with VLBI.
Methods: We observed a set of 13 strong sources (the S5 polar cap sample) at
8.4 and 15 GHz in phase-reference mode, with 32 different calibrator/target
combinations spanning angular separations between 1.5 and 20.5 degrees. We
obtained phase-referenced images and studied how the dynamic range and peak
flux density depend on observing frequency and source separation.
Results: We obtained dynamic ranges and peak flux densities of the
phase-referenced images as a function of frequency and separation from the
calibrator. We compared our results with models and phenomenological equations
previously reported.
Conclusions: The dynamic range of the phase-referenced images is strongly
limited by the atmosphere at all frequencies and for all source separations.
The limiting dynamic range is inversely proportional to the sine of the
calibrator-to-target separation. We also find that the peak flux densities,
relative to those obtained with the self-calibrated images, decrease with
source separation.Comment: 5 pages, 3 figures. Submitted to A&A on 5.02.2010; accepted on
11.03.2010
Radio emission of SN1993J. The complete picture: II. Simultaneous fit of expansion and radio light curves
We report on a simultaneous modelling of the expansion and radio light curves
of SN1993J. We have developed a simulation code capable of generating synthetic
expansion and radio light curves of supernovae by taking into consideration the
evolution of the expanding shock, magnetic fields, and relativistic electrons,
as well as the finite sensitivity of the interferometric arrays used in the
observations. Our software successfully fits all the available radio data of SN
1993J with an standard emission model for supernovae extended with some
physical considerations, as an evolution in the opacity of the ejecta material,
a radial drop of the magnetic fields inside the radiating region, and a
changing radial density profile of the circumstellar medium beyond day 3100
after explosion.Comment: 12 pages, 12 figures, accepted for publication in A&
First tests of the applicability of -ray imaging for background discrimination in time-of-flight neutron capture measurements
In this work we explore for the first time the applicability of using
-ray imaging in neutron capture measurements to identify and suppress
spatially localized background. For this aim, a pinhole gamma camera is
assembled, tested and characterized in terms of energy and spatial performance.
It consists of a monolithic CeBr scintillating crystal coupled to a
position-sensitive photomultiplier and readout through an integrated circuit
AMIC2GR. The pinhole collimator is a massive carven block of lead. A series of
dedicated measurements with calibrated sources and with a neutron beam incident
on a Au sample have been carried out at n_TOF, achieving an enhancement
of a factor of two in the signal-to-background ratio when selecting only those
events coming from the direction of the sample.Comment: Preprint submitted to Nucl. Instr. and Meth.
A Robotic Solution for the Restoration of Fresco Paintings
In this paper, a service robot solution is presented for the
analysis, surveying and restoration of fresco paintings. The
proposed design approach integrates robot design and
restoration operation. It aims to merge them into a feasible
solution that can be both practical and feasible for restorers.
The simulation results are reported to show a successful
design solution, which has been conceived with the
constraints of a low-cost user-oriented design and the
consideration of cultural heritage
Absolute kinematics of radio source components in the complete S5 polar cap sample. IV. Proper motions of the radio cores over a decade and spectral properties
We have carried out a high-precision astrometric analysis of two very-long-baseline-interferometry (VLBI) epochs of observation of the 13 extragalactic radio sources in the complete S5 polar cap sample. The VLBI epochs span a time baseline of 10 years and enable us to achieve precisions in the proper motions of the source cores up to a few micro-arcseconds per year. The observations were performed at 14.4 GHz and 43.1 GHz, and enable us to estimate the frequency core-shifts in a subset of sources, for which the spectral-index distributions can be computed. We study the source-position stability by analysing the changes in the relative positions of fiducial source points (the jet cores) over a decade. We find motions of 0.1-0.9 mas among close-by sources between the two epochs, which imply drifts in the jet cores of approximately a few tens of micro-as per year. These results have implications for the standard Active Galactic Nucleus (AGN) jet model (where the core locations are supposed to be stable in time). For one of our sources, 0615+820, the morphological and spectral properties in year 2010, as well as the relative astrometry between years 2000 and 2010, suggest the possibility of either a strong parsec-scale interaction of the AGN jet with the ISM, a gravitational lens with ~1 mas diameter, or a resolved massive binary black hole
Achondroplasia with 47, xxy karyotype: a case report of the neonatal diagnosis of an extremely unusual association
Background: The association of achondroplasia and Klinefelter syndrome is extremely rare. To date, five cases have
been previously reported, all of them diagnosed beyond the postnatal period, and only one was molecularly
characterized. We describe the first case of this unusual association diagnosed in the neonatal period, the clinical
findings and the molecular studies undertaken.
Case presentation: The boy was born at term with clinical and radiological features indicating the diagnosis of
achondroplasia or hypochondroplasia combined with the prenatal karyotype of Klinefelter syndrome (47,XXY).
Neonatal FGFR3 mutation screening showed that the newborn was heterozygous for the classic achondroplasia
G340R mutation. Microsatellite marker analysis showed that the sex chromosome aneuploidy had arisen from a
non-disjunction error in paternal meiosis I, with a recombination event in the pseudoautosomal region 1 (PAR1).
Conclusion: Specific mutation analysis is appropriate to confirm the clinical diagnosis of achondroplasia for
appropriate diagnosis, prognosis, and genetic counseling, especially when the karyotype does not explain the
abnormal prenatal sonographic findings. In the present case, a recombination event was observed in the PAR1
region, although recombinational events in paternally derived Klinefelter syndrome cases are much rarer than
expected
8.4GHz VLBI observations of SN2004et in NGC6946
We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of
the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20
February 2005 (151 days after explosion). The Very Large Array (VLA) flux
density was 1.230.07 mJy, corresponding to an isotropic luminosity at
8.4GHz of (4.450.3) erg s Hz and a brightness
temperature of (1.30.3) K. We also provide an improved
source position, accurate to about 0.5 mas in each coordinate. The VLBI image
shows a clear asymmetry. From model fitting of the size of the radio emission,
we estimate a minimum expansion velocity of 15,7002,000 km s. This
velocity is more than twice the expected mean expansion velocity estimated from
a synchrotron self-absorbed emission model, thus suggesting that synchrotron
self-absorption is not relevant for this supernova. With the benefit of an
optical spectrum obtained 12 days after explosion, we favor an emission model
which consists of two hot spots on an underlying expanding shell of width
comparable to that of SN 1993J.Comment: Accepted for publication in A&A (22/05/07
Radio emission of SN1993J: the complete picture. I. Re-analysis of all the available VLBI data
We have performed a complete re-calibration and re-analysis of all the
available VLBI observations of supernova SN1993J, following an homogeneous and
well-defined methodology. Observations of SN1993J at 69 epochs, spanning 13
years, were performed by two teams, which used different strategies and
analysis tools. The results obtained by each group are similar, but their
conclusions on the supernova expansion and the shape and evolution of the
emitting region differ significantly. From our analysis of the combined set of
observations, we have obtained an expansion curve with unprecedented time
resolution and coverage. We find that the data from both teams are compatible
when analyzed with the same methodology. One expansion index () is enough to model the expansion observed at 1.7\,GHz, while two
expansion indices ( and ), separated
by a break time, days, are needed to model the data, at
frequencies higher than 1.7\,GHz, up to day 4000 after explosion. We thus
confirm the wavelength dependence of the size of the emitting region reported
by one of the groups. We also find that all sizes measured at epochs later than
day 4000 after explosion are systematically smaller than our model predictions.
We estimate the fractional shell width (, average of all epochs
and frequencies) and the level of opacity to the radio emission by the ejecta.
We find evidence of a spectral-index radial gradient in the supernova shell,
which is indicative of a frequency-dependent ejecta opacity. Finally, we study
the distribution and evolution of the azimuthal anisotropies (hot spots) found
around the radio shell during the expansion. These anisotropies have
intensities of % of the mean flux density of the shell, and appear to
systematically evolve during the expansion.Comment: 13 pages, 9 figures, accepted for publication in A&
Absolute kinematics of radio source components in the complete S5 polar cap sample
We observed the thirteen extragalactic radio sources of the complete S5 polar
cap sample at 15.4 GHz with the Very Long Baseline Array, on 27 July 1999
(1999.57) and 15 June 2000 (2000.46). We present the maps from those two
epochs, along with maps obtained from observations of the 2 cm VLBA survey for
some of the sources of the sample, making a total of 40 maps. We discuss the
apparent morphological changes displayed by the radio sources between the
observing epochs. Our VLBA observations correspond to the first two epochs at
15.4 GHz of a program to study the absolute kinematics of the radio source
components of the members of the sample, by means of phase delay astrometry at
8.4 GHz, 15.4 GHz, and 43 GHz.
Our 15.4 GHz VLBA imaging allowed us to disentangle the inner milliarcsecond
structure of some of the sources, thus resolving components that appeared
blended at 8.4 GHz. For most of the sources, we identified the brightest
feature in each radio source with the core. These identifications are supported
by the spectral index estimates for those brightest features, which are in
general flat, or even inverted. Most of the sources display core-dominance in
the overall emission. We find that three of the sources have their most
inverted spectrum component shifted with respect to the origin in the map,
which approximately coincides with the peak-of-brightness at both 15.4 GHz and
8.4 GHz.Comment: Accepted by A&A (in press). 23 pages, 14 figure
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