The Gamma Cube: a new way to explore the gamma-ray sky

International audienceWe propose a new concept to allow the tracking of electrons in a gamma-ray telescope operating in the 5–100 MeV band. The idea of this experiment is to image the ionizing tracks that charged particles produce in a scintillator. It is a pair creation telescope at high energy and a Compton telescope with electron tracking at low energy. The telescope features a large scintillator transparent to the scintillation light, an ad-hoc optical system and a high resolution and highly sensitive imager. The performance perspectives and the advantages of such a system are outstanding but the technical difficulties are serious. A few years of research and development within the scientific community are required to reach the TRL level appropriate to propose the Gamma Cube in response to a flight opportunity

Contribution a l'etude de la cristallochimie et des proprietes electroniques des borures d'actinides

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Low Energy Characterization of Caliste HD, a Fine Pitch CdTe-Based Imaging Spectrometer

International audienceCaliste HD is a recently developed micro-camera designed for X and gamma-ray astronomy, based on a 1×1 cm$^2$ CdTe Schottky pixelated detector. Its entire surface is composed of 256 pixels, disposed on a 16 × 16 pixel array. This spectrometer is buttable on its 4 sides and can be used to create a large focal plane. It is also designed for space environment. Its IDeF-X front-end electronics has low power consumption, excellent noise performance and a wide dynamic range, from 2 keV to 1 MeV. Moreover, electronic noise performances of this device were optimized to set the low level energy threshold lower than 2 keV.This paper focuses on the Caliste HD performance near the low energy limit. For this purpose, we have exposed the CalisteHD module to a mono-energetic X-ray beam, and set energies between 2 and 12 keV. We measured accurately the detectionefficiency in this energy range and found it to be ranging from 39% to 75% for energies from 2.2 keV to 11.6 keV, consideringonly particles detected in the single-event photopeak and ignoring events impinging between two adjacent pixels. Thisefficiency detection profile thereby highlights crucial effects of the Pt electrode opacity on Caliste HD low energy response, andsuggests the presence of absorption zones at the interface between CdTe crystal and platinum. Respective thickness of eachlayer were estimated by simulation and confirmed by RBS ($Rutherford\ Backscattering\ Spectroscopy$).Besides, using a mono-energetic beam allows fine energy resolution measurement, which was found to be ranging from560 to 760 eV FWHM between 2 and 12 keV. In addition, the linearity of this spectrometer and the issue of charge sharingbetween adjacent pixels were studied. This study revealed that spectroscopic performances remain excellent for such boundaryoperating conditions

TARANIS XGRE and IDEE detection capability of terrestrial gamma-ray flashes and associated electron beams

International audienceWith a launch expected in 2018, the TARANIS microsatellite is dedicated to the study of transient phenomena observed in association with thunderstorms. On board the spacecraft, XGRE and IDEE are two instruments dedicated to studying terrestrial gamma-ray flashes (TGFs) and associated terrestrial electron beams (TEBs). XGRE can detect electrons (energy range: 1 to 10 MeV) and X- and gamma-rays (energy range: 20 keV to 10 MeV) with a very high counting capability (about 10 million counts per second) and the ability to discriminate one type of particle from another. The IDEE instrument is focused on electrons in the 80 keV to 4 MeV energy range, with the ability to estimate their pitch angles. Monte Carlo simulations of the TARANIS instruments, using a preliminary model of the spacecraft, allow sensitive area estimates for both instruments. This leads to an averaged effective area of 425 cm2 for XGRE, used to detect X- and gamma-rays from TGFs, and the combination of XGRE and IDEE gives an average effective area of 255 cm2 which can be used to detect electrons/positrons from TEBs. We then compare these performances to RHESSI, AGILE and Fermi GBM, using data extracted from literature for the TGF case and with the help of Monte Carlo simulations of their mass models for the TEB case. Combining this data with the help of the MC-PEPTITA Monte Carlo simulations of TGF propagation in the atmosphere, we build a self-consistent model of the TGF and TEB detection rates of RHESSI, AGILE and Fermi. It can then be used to estimate that TARANIS should detect about 200 TGFs yr-1 and 25 TEBs yr-1

TARANIS XGRE and IDEE Detection Capability of Terrestrial Gamma-Ray Flashes and Associated Electron Beams

Abstract. With a launch expected in 2018, the TARANIS microsatellite is dedicated to the study of transient phenomena observed in association with thunderstorms. On board the spacecraft, XGRE and IDEE are two instruments dedicated to studying terrestrial gamma-ray flashes (TGFs) and associated terrestrial electron beams (TEBs). XGRE can detect electrons (energy range: 1 to 10 MeV) and X- and gamma-rays (energy range: 20 keV to 10 MeV) with a very high counting capability (about 10 million counts per second) and the ability to discriminate one type of particle from another. The IDEE instrument is focused on electrons in the 80 keV to 4 MeV energy range, with the ability to estimate their pitch angles. Monte Carlo simulations of the TARANIS instruments, using a preliminary model of the spacecraft, allow sensitive area estimates for both instruments. This leads to an averaged effective area of 425 cm2 for XGRE, used to detect X- and gamma-rays from TGFs, and the combination of XGRE and IDEE gives an average effective area of 255 cm2 which can be used to detect electrons/positrons from TEBs. We then compare these performances to RHESSI, AGILE and Fermi GBM, using data extracted from literature for the TGF case and with the help of Monte Carlo simulations of their mass models for the TEB case. Combining this data with the help of the MC-PEPTITA Monte Carlo simulations of TGF propagation in the atmosphere, we build a self-consistent model of the TGF and TEB detection rates of RHESSI, AGILE and Fermi. It can then be used to estimate that TARANIS should detect about 200 TGFs yr−1 and 25 TEBs yr−1. </jats:p

FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG

We present the second catalog of high-energy γ-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely γ-ray-producing source classes