25 research outputs found
Polarisation measurements with a CdTe pixel array detector for Laue hard X-ray focusing telescopes
Polarimetry is an area of high energy astrophysics which is still relatively
unexplored, even though it is recognized that this type of measurement could
drastically increase our knowledge of the physics and geometry of high energy
sources. For this reason, in the context of the design of a Gamma-Ray Imager
based on new hard-X and soft gamma ray focusing optics for the next ESA Cosmic
Vision call for proposals (Cosmic Vision 2015-2025), it is important that this
capability should be implemented in the principal on-board instrumentation. For
the particular case of wide band-pass Laue optics we propose a focal plane
based on a thick pixelated CdTe detector operating with high efficiency between
60-600 keV. The high segmentation of this type of detector (1-2 mm pixel size)
and the good energy resolution (a few keV FWHM at 500 keV) will allow high
sensitivity polarisation measurements (a few % for a 10 mCrab source in 106s)
to be performed. We have evaluated the modulation Q factors and minimum
detectable polarisation through the use of Monte Carlo simulations (based on
the GEANT 4 toolkit) for on and off-axis sources with power law emission
spectra using the point spread function of a Laue lens in a feasible
configuration.Comment: 10 pages, 6 pages. Accepted for publication in Experimental Astronom
Dual-Cathode CsI Covered Microstrip Plate as VUV High Efficiency Photosensor
A Gas Proportional Scintillation Counter based on a dual-cathode Microstrip Plate covered with a CsI film is described. This new dual-cathode technique has the advantage of increasing the VUV sensitive area of the Microstrip Plate. A detailed description of the technique is presented together with a discussion of the performance. The results obtained for a xenon filled Gas Proportional Scintillation Counter show an improvement of the energy resolution for 5.9 keV X-rays from 12.7%, for a single cathode device, to 11.1% for the dual-cathode devic
Cadmium (zinc) telluride 2D/3D spectrometers for scattering polarimetry
he semiconductor detectors technology has dramatically changed the broad field of x- and γ-rays spectroscopy and imaging. Semiconductor detectors, originally developed for particle physics applications, are now widely used for x/γ-rays spectroscopy and imaging in a large variety of fields, among which, for example, x-ray fluorescence, γ-ray monitoring and localization, noninvasive inspection and analysis, astronomy, and diagnostic medicine. The success of semiconductor detectors is due to several unique 242characteristics as the excellent energy resolution, the high detection efficiency, and the possibility of development of compact and highly segmented detection systems (i.e., spectroscopic imager). Among the semiconductor devices, silicon (Si) detectors are the key detectors in the soft x-ray band (15 keV) and will continue to be the first choice for laboratory-based high-performance spectrometers system (Eberth and Simpson 2006)
A focal plane detector design for a wide-band Laue-lens telescope
The energy range above 60 keV is important for the study of many open
problems in high energy astrophysics such as the role of Inverse Compton with
respect to synchrotron or thermal processes in GRBs, non thermal mechanisms in
SNR, the study of the high energy cut-offs in AGN spectra, and the detection of
nuclear and annihilation lines. Recently the development of high energy Laue
lenses with broad energy bandpasses from 60 to 600 keV have been proposed for a
Hard X ray focusing Telescope (HAXTEL) in order to study the X-ray continuum of
celestial sources. The required focal plane detector should have high detection
efficiency over the entire operative range, a spatial resolution of about 1 mm,
an energy resolution of a few keV at 500 keV and a sensitivity to linear
polarization. We describe a possible configuration of the focal plane detector
based on several CdTe/CZT pixelated layers stacked together to achieve the
required detection efficiency at high energy. Each layer can operate both as a
separate position sensitive detector and polarimeter or work with other layers
to increase the overall photopeak efficiency. Each layer has a hexagonal shape
in order to minimize the detector surface required to cover the lens field of
view. The pixels would have the same geometry so as to provide the best
coupling with the lens point spread function and to increase the symmetry for
polarimetric studies.Comment: 10 pages, 9 figure
A Balloon-Borne 3D CZT Scattering Polarimeter for Hard X-Ray Astrophysics
It is widely recognised that a measurement of the polarization of the high energy emission from cosmic sources is a key observational parameter which will aid in the understanding of the nature of high energy cosmic ray astrophysics. Therefore new instrumentation operating in this energy range should exhibit a good sensitivity also for this type of measurements Herein we present the concept of a small high performance detector optimized for polarimetry between 100 and 500 keV suitable for use with a stratospheric balloon-borne payload dedicated to obtaining accurate measurements of the polarization of the Crab pulsar. The detector with 3D spatial resolution is based on CZT spectrometer sensitive units in a highly segmented configuration suitable for operation as a high quality scattering polarimeter. We describe recent development results and possible improvement currently under study. The proposed payload can be also considered as a pathfinder for a high performance focal plane detector for the next generation of hard X and soft gamma ray telescopes based on Laue lenses
Constituição Anotada da República Democrática de Timor-Leste
A independência de Timor-Leste, proclamada pela Frente Revolucionária do
Timor-Leste Independente (FRETILIN) em 28 de novembro de 1975, vê-se
internacionalmente reconhecida a 20 de maio de 2002, uma vez concretizada
a libertação do povo timorense da colonização e da ocupação ilegal da Pátria
Maubere por potências estrangeiras.
A elaboração e adoção da Constituição da República Democrática de Timor-
-Leste culminam a secular resistência do povo timorense, intensificada com a
invasão de 7 de dezembro de 1975.
A luta travada contra o inimigo, inicialmente sob a liderança da FRETILIN,
deu lugar a formas mais abrangentes de participação política, com a criação
sucessiva do Conselho Nacional de Resistência Maubere (CNRM), em 1987, e
do Conselho Nacional de Resistência Timorense (CNRT), em 1998.
A Resistência desdobrou-se em três frentes.
A frente armada foi protagonizada pelas gloriosas Forças Armadas de Libertação
Nacional de Timor-Leste (FALINTIL), cuja gesta histórica cabe exaltar.
A ação da frente clandestina, astutamente desencadeada em território hostil,
envolveu o sacrifício de milhares de vidas de mulheres e homens, em especial
jovens, que lutaram com abnegação em prol da liberdade e independência.
A frente diplomática, conjugadamente desenvolvida em todo o Mundo, permitiu
abrir caminho para a libertação definitiva.
Na sua vertente cultural e humana, a Igreja Católica em Timor-Leste sempre
soube assumir com dignidade o sofrimento de todo o Povo, colocando-se ao
seu lado na defesa dos seus mais elementares direitos. Esta Constituição representa,
finalmente, uma sentida homenagem a todos os mártires da Pátria.
Assim, os Deputados da Assembleia Constituinte, legítimos representantes
do Povo eleitos a 30 de agosto de 2001; Alicerçados ainda no ato referendário de 30 de agosto de 1999, que, concretizado
sob os auspícios da Organização das Nações Unidas, confirmou a
vontade autodeterminada de independência;
Plenamente conscientes da necessidade de se erigir uma cultura democrática
e institucional própria de um Estado de Direito onde o respeito pela Constituição,
pelas leis e pelas instituições democraticamente eleitas sejam a sua
base inquestionável;
Interpretando o profundo sentimento, as aspirações e a fé em Deus do povo
de Timor-Leste;
Reafirmam solenemente a sua determinação em combater todas as formas
de tirania, opressão, dominação e segregação social, cultural ou religiosa,
defender a independência nacional, respeitar e garantir os direitos humanos
e os direitos fundamentais do cidadão, assegurar o princípio da separação de
poderes na organização do Estado e estabelecer as regras essenciais da democracia
pluralista, tendo em vista a construção de um país justo e próspero e o
desenvolvimento de uma sociedade solidária e fraterna.
A Assembleia Constituinte, reunida na sessão plenária de 22 de março de
2002, aprova e decreta a seguinte Constituição da República Democrática de
Timor-Leste
XIPE: the X-ray Imaging Polarimetry Explorer
X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and
temporal variability measurements and to imaging, allows a wealth of physical
phenomena in astrophysics to be studied. X-ray polarimetry investigates the
acceleration process, for example, including those typical of magnetic
reconnection in solar flares, but also emission in the strong magnetic fields
of neutron stars and white dwarfs. It detects scattering in asymmetric
structures such as accretion disks and columns, and in the so-called molecular
torus and ionization cones. In addition, it allows fundamental physics in
regimes of gravity and of magnetic field intensity not accessible to
experiments on the Earth to be probed. Finally, models that describe
fundamental interactions (e.g. quantum gravity and the extension of the
Standard Model) can be tested. We describe in this paper the X-ray Imaging
Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a
small mission with a launch in 2017 but not selected. XIPE is composed of two
out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD)
filled with a He-DME mixture at their focus and two additional GPDs filled with
pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 %
at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half
Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X
optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with
Malindi as down-link station and of a Mission Operation Center (MOC) at INPE
(Brazil).Comment: 49 pages, 14 figures, 6 tables. Paper published in Experimental
Astronomy http://link.springer.com/journal/1068
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is
designed to identify and characterize gamma rays from extreme explosions and
accelerators. The main science themes include: supermassive black holes and
their connections to neutrinos and cosmic rays; binary neutron star mergers and
the relativistic jets they produce; cosmic ray particle acceleration sources
including Galactic supernovae; and continuous monitoring of other astrophysical
events and sources over the full sky in this important energy range. AMEGO-X
will probe the medium energy gamma-ray band using a single instrument with
sensitivity up to an order of magnitude greater than previous telescopes in the
energy range 100 keV to 1 GeV that can be only realized in space. During its
three-year baseline mission, AMEGO-X will observe nearly the entire sky every
two orbits, building up a sensitive all-sky map of gamma-ray sources and
emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of
Opportunity.Comment: 23 pages, 16 figures, Published Journal of Astronomical Telescopes,
Instruments, and System
All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class
mission concept that will provide essential contributions to multimessenger
astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in
the 200 keV to 10 GeV energy range with a wide field of view, good spectral
resolution, and polarization sensitivity. Therefore, AMEGO is key in the study
of multimessenger astrophysical objects that have unique signatures in the
gamma-ray regime, such as neutron star mergers, supernovae, and flaring active
galactic nuclei. The order-of-magnitude improvement compared to previous MeV
missions also enables discoveries of a wide range of phenomena whose energy
output peaks in the relatively unexplored medium-energy gamma-ray band