428 research outputs found
Mapping the Milky Way bulge at high resolution: the 3D dust extinction, CO, and X factor maps
Three dimensional interstellar extinction maps provide a powerful tool for
stellar population analysis. We use data from the VISTA Variables in the Via
Lactea survey together with the Besan\c{c}on stellar population synthesis model
of the Galaxy to determine interstellar extinction as a function of distance in
the Galactic bulge covering and . We adopted a
recently developed method to calculate the colour excess. First we constructed
the H-Ks vs. Ks and J-Ks vs. Ks colour-magnitude diagrams based on the VVV
catalogues that matched 2MASS. Then, based on the temperature-colour relation
for M giants and the distance-colour relations, we derived the extinction as a
function of distance. The observed colours were shifted to match the intrinsic
colours in the Besan\c{c}on model as a function of distance iteratively. This
created an extinction map with three dimensions: two spatial and one distance
dimension along each line of sight towards the bulge. We present a 3D
extinction map that covers the whole VVV area with a resolution of 6' x 6',
using distance bins of 0.5 kpc. The high resolution and depth of the photometry
allows us to derive extinction maps for a range of distances up to 10 kpc and
up to 30 magnitudes of extinction in . Integrated maps show the same
dust features and consistent values as other 2D maps. We discuss the spatial
distribution of dust features in the line of sight, which suggests that there
is much material in front of the Galactic bar, specifically between 5-7 kpc. We
compare our dust extinction map with high-resolution maps towards
the Galactic bulge, where we find a good correlation between and
. We determine the X factor by combining the CO map and our dust
extinction map. Our derived average value is consistent with the canonical
value of the Milky Way.Comment: 11 pages, 18 figures, accepted for publication in
Astronomy&Astrophysic
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments
carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on
2000 October 9. HETE-2 is an international mission consisting of a small
satellite dedicated to provide broad-band observations and accurate
localizations of gamma-ray bursts (GRBs). A unique feature of this mission is
its capability to determine and transmit GRB coordinates in almost real-time
through the burst alert network. The WXM consists of three elements: four
identical Xe-filled one-dimensional position-sensitive proportional counters,
two sets of one-dimensional coded apertures, and the main electronics. The WXM
counters are sensitive to X-rays between 2 keV and 25 keV within a
field-of-view of about 1.5 sr, with a total detector area of about 350 cm.
The in-flight triggering and localization capability can produce a real-time
GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
erg cm. In this report, the details of the mechanical
structure, electronics, on-board software, ground and in-flight calibration,
and in-flight performance of the WXM are discussed.Comment: 28 pages, 24 figure
Measurement of forward photon production cross-section in proton-proton collisions at = 13 TeV with the LHCf detector
In this paper, we report the production cross-section of forward photons in
the pseudorapidity regions of and ,
measured by the LHCf experiment with proton--proton collisions at =
13 TeV. The results from the analysis of 0.191 of data
obtained in June 2015 are compared to the predictions of several hadronic
interaction models that are used in air-shower simulations for
ultra-high-energy cosmic rays. Although none of the models agree perfectly with
the data, EPOS-LHC shows the best agreement with the experimental data among
the models.Comment: 21 pages, 4 figure
Catalogue of high-mass X-ray binaries in the Galaxy ( edition)
We present a new edition of the catalogue of high-mass X-ray binaries in the
Galaxy. The catalogue contains source name(s), coordinates, finding chart,
X-ray luminosity, system parameters, and stellar parameters of the components
and other characteristic properties of 114 high-mass X-ray binaries, together
with a comprehensive selection of the relevant literature. The aim of this
catalogue is to provide the reader with some basic information on the X-ray
sources and their counterparts in other wavelength ranges (-rays, UV,
optical, IR, radio). About 60% of the high-mass X-ray binary candidates are
known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries.
Some sources, however, are only tentatively identified as high-mass X-ray
binaries on the basis of their X-ray properties similar to the known high-mass
X-ray binaries. Further identification in other wavelength bands is needed to
finally determine the nature of these sources. In cases where there is some
doubt about the high-mass nature of the X-ray binary this is mentioned.
Literature published before 1 October 2005 has, as far as possible, been taken
into account.Comment: 25 pages, table include
HETE Observations of the Gamma-Ray Burst GRB030329: Evidence for an Underlying Soft X-ray Component
An exceptionally intense gamma-ray burst, GRB030329, was detected and
localized by the instruments on board the High Energy Transient Explorer
satellite (HETE) at 11:37:14 UT on 29 March 2003. The burst consisted of two
\~10s pulses of roughly equal brightness and an X-ray tail lasting >100s. The
energy fluence in the 30-400 keV energy band was 1.08e-4 erg/cm2, making
GRB030329 one of the brightest GRBs ever detected. Communication of a 2 arcmin
error box 73 minutes after the burst allowed the rapid detection of a
counterpart in the optical, X-ray, radio and the ensuing discovery of a
supernova with most unusual characteristics. Analyses of the burst lightcurves
reveal the presence of a distinct, bright, soft X-ray component underlying the
main GRB: the 2-10 keV fluence of this component is ~7e-6 erg/cm2. The main
pulses of GRB030329 were preceded by two soft, faint, non-thermal bumps. We
present details of the HETE observations of GRB030329.Comment: 22 pages, 5 figures, to be published in ApJ 617, no. 2 (10 December
2004). Referee comments have been incorporated; results of improved spectral
analysis are include
Global Characteristics of X-Ray Flashes and X-Ray-Rich GRBs Observed by HETE-2
We describe and discuss the global properties of 45 gamma-ray bursts (GRBs)
observed by HETE-2 during the first three years of its mission, focusing on the
properties of X-Ray Flashes (XRFs) and X-ray-rich GRBs (XRRs). We find that the
numbers of XRFs, XRRs, and GRBs are comparable. We find that the durations and
the sky distributions of XRFs and XRRs are similar to those of GRBs. We also
find that the spectral properties of XRFs and XRRs are similar to those of
GRBs, except that the values of the peak energy of the
burst spectrum in , the peak energy flux \Fp, and the energy
fluence of XRFs are much smaller -- and those of XRRs are smaller -- than
those of GRBs. Finally, we find that the distributions of all three kinds of
bursts form a continuum in the [(2-30 keV),(30-400) keV]-plane, the
[(2-400 keV), ]-plane, and the [(50-300 keV),
]-plane. These results provide strong evidence that all three
kinds of bursts arise from the same phenomenon.Comment: 33 pages, 15 figures, submitted to Ap
CARDIAN: a novel computational approach for real-time end-diastolic frame detection in intravascular ultrasound using bidirectional attention networks
INTRODUCTION:
Changes in coronary artery luminal dimensions during the cardiac cycle can impact the accurate quantification of volumetric analyses in intravascular ultrasound (IVUS) image studies. Accurate ED-frame detection is pivotal for guiding interventional decisions, optimizing therapeutic interventions, and ensuring standardized volumetric analysis in research studies. Images acquired at different phases of the cardiac cycle may also lead to inaccurate quantification of atheroma volume due to the longitudinal motion of the catheter in relation to the vessel. As IVUS images are acquired throughout the cardiac cycle, end-diastolic frames are typically identified retrospectively by human analysts to minimize motion artefacts and enable more accurate and reproducible volumetric analysis.
METHODS:
In this paper, a novel neural network-based approach for accurate end-diastolic frame detection in IVUS sequences is proposed, trained using electrocardiogram (ECG) signals acquired synchronously during IVUS acquisition. The framework integrates dedicated motion encoders and a bidirectional attention recurrent network (BARNet) with a temporal difference encoder to extract frame-by-frame motion features corresponding to the phases of the cardiac cycle. In addition, a spatiotemporal rotation encoder is included to capture the IVUS catheter's rotational movement with respect to the coronary artery.
RESULTS:
With a prediction tolerance range of 66.7â
ms, the proposed approach was able to find 71.9%, 67.8%, and 69.9% of end-diastolic frames in the left anterior descending, left circumflex and right coronary arteries, respectively, when tested against ECG estimations. When the result was compared with two expert analystsâ estimation, the approach achieved a superior performance.
DISCUSSION:
These findings indicate that the developed methodology is accurate and fully reproducible and therefore it should be preferred over experts for end-diastolic frame detection in IVUS sequences
HETE-2 Observation of two gamma-ray bursts at z > 3
GRB 020124 and GRB 030323 constitute half the sample of gamma-ray bursts with
a measured redshift greater than 3. This paper presents the temporal and
spectral properties of these two gamma-ray bursts detected and localized with
HETE-2. While they have nearly identical redshifts (z=3.20 for GRB 020124, and
z=3.37 for GRB 030323), these two GRBs span about an order of magnitude in
fluence, thus sampling distinct regions of the GRB luminosity function. The
properties of these two bursts are compared with those of the bulk of the GRB
population detected by HETE-2. We also discuss the energetics of GRB 020124 and
GRB 030323 and show that they are compatible with the Epeak - Eiso relation
discovered by Amati et al. (2002). Finally, we compute the maximum redshifts at
which these bursts could have been detected by HETE-2 and we address various
issues connected with the detection and localization of high-z GRBs.Comment: 19 pages, 4 figures, submitted to Ap
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