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)

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

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

Etude de polarimètres basés sur les détecteurs CdTe en astrophysique X et gamma

Au-delà d'énergies supérieures à 10 keV aucun instrument n'a effectué des mesures polarimétriques en astrophysique. Grâce à une collaboration étroite entre le Laboratoire IASF, CNR, Bologne (Italie) et le Laboratoire PHASE du CNRS de Strasbourg nous avons étudié à la fois par des simulations et par des mesures physiques les possibilités offertes par des polarimètres basés sur les détecteurs CdTe en astrophysique X et g. L'essentiel de ce travail a porté sur l'étude et le développement du projet d'un polarimètre pour le domaine X et g: le télescope CIPHER (Coded Imager and Polarimeter for High Energy Radiaton).Le principe des polarimètres étudiés se base sur la diffusion Compton, car il existe une dépendance angulaire de la direction des photons émergeants après l'interaction par rapport à la direction du vecteur polarisation des photons du faisceau incident. Des simulations du plan de détection de l'instrument ont été réalisées et une expérience de validation a été effectuée à l'ESRF à Grenoble à partir de matrices monolithiques pixélisées (44 pixels) à base de CdTe. A partir des calculs réalisés pour le polarimètre CIPHER sont obtenus des facteurs polarimétriques Q supérieurs à 0,5 et des efficacités relatives de détection d'événements doubles d'environ 20% dans la gamme d'énergie entre 100 keV et 1 MeV. Les mesures effectuées à partir de matrices monolithiques de CdTe de 44 pixels testées à l'ESRF à Grenoble vérifient en bonne approximation ces performances (Q 0,4 à 300 keV et efficacités supérieures à 20 %). L'ensemble de ces résultats place potentiellement le télescope CIPHER parmi les instruments les plus performants dans le domaine de la polarimétrie des rayons X de haute énergie et des g de faible énergie.Polarimetry in astronomy for hard X- and soft g-ray energy range had no much development up to date. Therefore a collaboration project was developed between the Laboratoire PHASE, CNRS, Strasbourg, France and the IASF, CNR, Italy, in order to study the polarimetric capabilities of CdTe based detectors for polarimetry in astrophysics through Monte Carlo simulations and experimental measurements. Herein we proposed and studied a polarimeter for hard X-ray and soft g-ray astrophysical sources known as the CIPHER (Coded Imager and Polarimeter for High Energy Radiation) telescope.In this energy range the principle of operation of polarimeters is based on Compton scattering, since there is a dependency between the direction of the emerging Compton photons and the initial photon beam polarisation vector direction. As part of the design process of the detection plane, a sophisticated Monte Carlo simulation code was developed and a pixelated CdTe monolithic matrix (44 pixels) was tested at the ESRF in Grenoble, France, in order to verify the simulation model. Simulations shown that this instrument can potentially present polarimetric Q factors higher than and double events relative efficiencies of about 20 % from 100 keV to 1 MeV energy range. The polarimetric measurements for a CdTe semiconductor detector of 44 pixels carried out at the ESRF were in good agreement with these performances (Q 0.4 @ 300 keV and efficiencies higher than 20 %). From both results we can conclude that CIPHER telescope is potentially among the instruments that present better performances in hard X- and soft g-ray polarimetry.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Hard X-ray and Soft Gamma Ray Polarimetry with CdTe/CZT Spectro-Imager

CdTe/CZT based spectroscopic two-dimensional (2D)/three-dimensional (3D) imagers when operated in the Compton regime can work as high performance scattering polarimeters, for high-energy astrophysics. Polarimetry in high-energy astrophysics has been little explored. To date, X- and γ-ray source emissions have been studied almost exclusively through spectral, imaging, and timing analysis. Polarization measurements provide two additional observational parameters: the polarization angle and the level of linear polarization. These additional parameters should allow for a better discrimination between the physical mechanisms of different emission models characterizing a celestial object. Therefore, polarimetry will play a strategic role in new instrumentations for future high-energy astronomy missions. 2D and 3D CZT/CdTe spectroscopic imagers provided with coincidence readout logic can efficiently handle scattering events to perform simultaneously polarization, spectroscopy, imaging, and timing measurements. Herein, we describe the results obtained, both experimentally and by MC simulations, with CdTe/CZT pixel detector prototypes in high-energy polarimetry. We give an overview on the achievable polarimetric performance with spectroscopic imagers and on how these performances are affected by detector configuration parameters. Finally, we address the perspective of scattering polarimetry opened by the recent implementation of new high energy focusing optics, as broadband Laue lens, in next generation of hard X- and soft γ-ray astronomy instrumentation. The unprecedented sensitivity achievable by these telescopes will definitely open the window of polarimetry in this high-energy range