286 research outputs found
ORIGAMIX, a CdTe-based spectro-imager development for nuclear applications
The Astrophysics Division of CEA Saclay has a long history in the development
of CdTe based pixelated detection planes for X and gamma-ray astronomy, with
time-resolved imaging and spectrometric capabilities. The last generation,
named Caliste HD, is an all-in-one modular instrument that fulfills
requirements for space applications. Its full-custom front-end electronics is
designed to work over a large energy range from 2 keV to 1 MeV with excellent
spectroscopic performances, in particular between 10 and 100 keV (0.56 keV FWHM
and 0.67 keV FWHM at 13.9 and 59.5 keV). In the frame of the ORIGAMIX project,
a consortium based on research laboratories and industrials has been settled in
order to develop a new generation of gamma camera. The aim is to develop a
system based on the Caliste architecture for post-accidental interventions or
homeland security, but integrating new properties (advanced spectrometry,
hybrid working mode) and suitable for industry. A first prototype was designed
and tested to acquire feedback for further developments. In this study, we
particularly focused on spectrometric performances with high energies and high
fluxes. Therefore, our device was exposed to energies up to 700 keV (133Ba,
137Cs) and we measured the evolution of energy resolution (0.96 keV at 80 keV,
2.18 keV at 356 keV, 3.33 keV at 662 keV). Detection efficiency decreases after
150 keV, as Compton effect becomes dominant. However, CALISTE is also designed
to handle multiple events, enabling Compton scattering reconstruction, which
can drastically improve detection efficiencies and dynamic range for higher
energies up to 1408 keV (22Na, 60Co, 152Eu) within a 1-mm thick detector. In
particular, such spectrometric performances obtained with 152Eu and 60Co were
never measured before with this kind of detector.Comment: Nuclear Instruments and Methods in Physics Research Section A:
Accelerators, Spectrometers, Detectors and Associated Equipment. Available
online 9 January 2015, ISSN 0168-9002
(http://www.sciencedirect.com/science/article/pii/S0168900215000133).
Keywords: CdTe; X-ray; Gamma-ray; Spectrometry; Charge-sharing; Astrophysics
Instrumentation; Nuclear Instrumentation; Gamma-ray camera
SVOM pointing strategy: how to optimize the redshift measurements?
The Sino-French SVOM mission (Space-based multi-band astronomical Variable
Objects Monitor) has been designed to detect all known types of gamma-ray
bursts (GRBs) and to provide fast and reliable GRB positions. In this study we
present the SVOM pointing strategy which should ensure the largest number of
localized bursts allowing a redshift measurement. The redshift measurement can
only be performed by large telescopes located on Earth. The best scientific
return will be achieved if we are able to combine constraints from both space
segment (platform and payload) and ground telescopes (visibility).Comment: Proceedings of Gamma-Ray Bursts 2007 conference, Santa Fe, USA, 5-9
November 2007. Published in AIP conf. proc. 1000, 585-588 (2008
The ECLAIRs micro-satellite mission for gamma-ray burst multi-wavelength observations
Gamma-ray bursts (GRB), at least those with a duration longer than a few
seconds are the most energetic events in the Universe and occur at cosmological
distances. The ECLAIRs micro-satellite, to be launched in 2009, will provide
multi-wavelength observations of GRB, to study their astrophysics and to use
them as cosmological probes. Furthermore in 2009 ECLAIRs is expected to be the
only space borne instrument capable of providing a GRB trigger in near
real-time with sufficient localization accuracy for GRB follow-up observations
with the powerful ground based spectroscopic telescopes available by then. A
"Phase A study" of the ECLAIRs project has recently been launched by the French
Space Agency CNES, aiming at a detailed mission design and selection for flight
in 2006. The ECLAIRs mission is based on a CNES micro-satellite of the
"Myriade" family and dedicated ground-based optical telescopes. The satellite
payload combines a 2 sr field-of-view coded aperture mask gamma-camera using
6400 CdTe pixels for GRB detection and localization with 10 arcmin precision in
the 4 to 50 keV energy band, together with a soft X-ray camera for onboard
position refinement to 1 arcmin. The ground-based optical robotic telescopes
will detect the GRB prompt/early afterglow emission and localize the event to
arcsec accuracy, for spectroscopic follow-up observations.Comment: 7 pages, 1 figure, proceedings of the conference "New Developments in
Photodetection", Beaune (France), June 25005. Submitted to NIM-A (Elsevier
Science
The digital data processing concepts of the LOFT mission
The Large Observatory for X-ray Timing (LOFT) is one of the five mission
candidates that were considered by ESA for an M3 mission (with a launch
opportunity in 2022 - 2024). LOFT features two instruments: the Large Area
Detector (LAD) and the Wide Field Monitor (WFM). The LAD is a 10 m 2 -class
instrument with approximately 15 times the collecting area of the largest
timing mission so far (RXTE) for the first time combined with CCD-class
spectral resolution. The WFM will continuously monitor the sky and recognise
changes in source states, detect transient and bursting phenomena and will
allow the mission to respond to this. Observing the brightest X-ray sources
with the effective area of the LAD leads to enormous data rates that need to be
processed on several levels, filtered and compressed in real-time already on
board. The WFM data processing on the other hand puts rather low constraints on
the data rate but requires algorithms to find the photon interaction location
on the detector and then to deconvolve the detector image in order to obtain
the sky coordinates of observed transient sources. In the following, we want to
give an overview of the data handling concepts that were developed during the
study phase.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
The LOFT Burst Alert System and its Burst On-board Trigger
The ESA M3 candidate mission LOFT (Large Observatory For x-ray Timing) has
been designed to study strong gravitational fields by observing compact
objects, such as black-hole binaries or neutron-star systems and supermassive
black-holes, based on the temporal analysis of photons collected by the primary
instrument LAD (Large Area Detector), sensitive to X-rays from 2 to 50 keV,
offering a very large effective area (>10 m 2 ), but a small field of view
({\o}<1{\deg}). Simultaneously the second instrument WFM (Wide Field Monitor),
composed of 5 coded-mask camera pairs (2-50 keV), monitors a large part of the
sky, in order to detect and localize eruptive sources, to be observed with the
LAD after ground-commanded satellite repointing. With its large field of view
(>{\pi} sr), the WFM actually detects all types of transient sources, including
Gamma-Ray Bursts (GRBs), which are of primary interest for a world-wide
observers community. However, observing the quickly decaying GRB afterglows
with ground-based telescopes needs the rapid knowledge of their precise
localization. The task of the Loft Burst Alert System (LBAS) is therefore to
detect in near- real-time GRBs (about 120 detections expected per year) and
other transient sources, and to deliver their localization in less than 30
seconds to the observers, via a VHF antenna network. Real-time full resolution
data download to ground being impossible, the real-time data processing is
performed onboard by the LBOT (LOFT Burst On-board Trigger system). In this
article we present the LBAS and its components, the LBOT and the associated
ground-segment.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM
The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low
Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based
multi-band astronomical Variable Objects Monitor), a French-Chinese mission
with Italian contribution. Observations are expected to start in 2013. It has
been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent
sources of the sky, thanks to its wide field of view (about 2 sr) and its
remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging
sensitivity in the 4-70 keV energy band. These characteristics are well suited
to detect highly redshifted GRBs, and consequently to provide fast and accurate
triggers to other onboard or ground-based instruments able to follow-up the
detected events in a very short time from the optical wavelength bands up to
the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008,
Nanjing, Chin
Multimodal Highlighting of Structural Abnormalities in Diabetic Rat and Human Corneas.
PURPOSE: This study aimed to highlight structural corneal changes in a model of type 2 diabetes, using in vivo corneal confocal microscopy (CCM). The abnormalities were also characterized by transmission electron microscopy (TEM) and second harmonic generation (SHG) microscopy in rat and human corneas.
METHODS: Goto-Kakizaki (GK) rats were observed at age 12 weeks (n = 3) and 1 year (n = 6), and compared to age-matched controls. After in vivo CCM examination, TEM and SHG microscopy were used to characterize the ultrastructure and the three-dimensional organization of the abnormalities. Human corneas from diabetic (n = 3) and nondiabetic (n = 3) patients were also included in the study.
RESULTS: In the basal epithelium of GK rats, CCM revealed focal hyper-reflective areas, and histology showed proliferative cells with irregular basement membrane. In the anterior stroma, extracellular matrix modifications were detected by CCM and confirmed in histology. In the Descemet's membrane periphery of all the diabetic corneas, hyper-reflective deposits were highlighted using CCM and characterized as long-spacing collagen fibrils by TEM. SHG microscopy revealed these deposits with high contrast, allowing specific detection in diabetic human and rat corneas without preparation and characterization of their three-dimensional organization.
CONCLUSION: Pathologic findings were observed early in the development of diabetes in GK rats. Similar abnormalities have been found in corneas from diabetic patients.
TRANSLATIONAL RELEVANCE: This multidisciplinary study highlights diabetes-induced corneal abnormalities in an animal model, but also in diabetic donors. This could constitute a potential early marker for diagnosis of hyperglycemia-induced tissue changes
IGR J08408--4503: a new recurrent Supergiant Fast X-ray Transient
The supergiant fast X-ray transient IGR J08408-4503 was discovered by
INTEGRAL on May 15, 2006, during a bright flare. The source shows sporadic
recurrent short bright flares, reaching a peak luminosity of 10^36 erg s^-1
within less than one hour. The companion star is HD 74194, an Ob5Ib(f)
supergiant star located at 3 kpc in the Vela region. We report the light curves
and broad-band spectra (0.1-200 keV) of all the three flares of IGR J08408-4503
detected up to now based on INTEGRAL and Swift data. The flare spectra are well
described by a power-law model with a high energy cut-off at ~15 keV. The
absorption column density during the flares was found to be ~10^21 cm^-2,
indicating a very low matter density around the compact object. Using the
supergiant donor star parameters, the wind accretion conditions imply an
orbital period of the order of one year, a spin period of the order of hours
and a magnetic field of the order of 10^13 G.Comment: 5 pages, 2 figures, accepted for publication in Astrophysical Journal
Letter
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