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ECLAIRs, a 2-D coded-mask imaging camera on-board the Sino-French SVOM space missi on, will detect and locate gamma-ray bursts in near real time in the 4 - 150 keV energy band in a large field of view. The design of ECLAIRs has been driven by the objective to reach an unprecedented low-energy threshold of 4 keV. The detection plane is an assembly of 6400 Schottky CdTe detectors of size 4x4x1 mm 3 , biased from -200V to -500V and operated at -20°C. The low-energy threshold is achieved thanks to an innovative hybrid module composed of a thick film ceramic holding 32 CdTe detectors ("Detectors Ceramics"), associated to an HTCC ceramic housing a low-noise 32-channel ASIC ("ASIC Ceramics"). We manage the coupling between Detectors Ceramics and ASIC Ceramics in order to achieve the best performance and ensure the unifor mity of the detection plane. In this paper, we describe the complete hybrid XRDPIX, of which 50 flight models have been manufactured by the SAGEM company. Afterwards, we show test results obtained on Detectors Ceramics, on ASIC Ceramics and on the modules once assembled. Then, we compare and confront detectors leakage currents and ASIC ENC with the energy threshold values and FWHM measured on XRDPIX modules at the temperature of -20°C by using a calibrated radioactive source of 241Am. Finally, we study the homogeneity of the spectral properties of the 32-detector hybrid matrices and we conclude on general performance of more than 1000 detection channels which may reach the low-energy threshold of 4 keV required for the future ECLAIRs space camera.

Ohmic CdZnTe and CdTe detectors have been successfully used in high-energy missions such as IBIS on-board INTEGRAL and the Swift-BAT in the past two decades. Such detectors provide very good quantum efficiency in the hard X-ray band. For the future generation of hard X-ray coded mask detectors, a higher sensitivity will be required. A way to achieve this is to increase the effective area of the pixilated detection plane, to change the mask pattern and/or the properties of the semi-conductors paving the detection plane. For the future Chinese-French Gamma-ray burst mission SVOM, the GRB trigger camera ECLAIRs will make use of a new type of high-energy detectors, the Schottky CdTe detectors. Such detectors, when reversely biased, are known to present very low leakage current, resulting in lower values of the low-energy threshold (down to 4 keV or less) than for previous missions (i.e. > 10 keV for the Swift-BAT and INTEGRAL/IBIS). Such low values will enable ECLAIRs with a moderate geometrical area of 1024 cm2 and a low-energy threshold of 4 keV to be more sensitive to high-redshift GRBs (emitting mainly in X-rays) than the Swift-BAT with a higher effective area and low-energy threshold. However, the spectral performance of such detectors are known to degrade over time, once polarized, due to the polarization effect that strongly depends on the temperature and the bias voltage applied to the detectors. In this paper, we present an intensive study of the properties of Schottky CdTe detectors as used on SVOM/ECLAIRs such as I-V characteristics, polarization effect, activation energy and low temperature annealing effects. We discuss the implications of these measurements on the use of this type of detectors in future high-energy instruments.

ECLAIRs, a 2-D coded-mask imaging camera on-board the Sino-French SVOM space mission, will detect and locate Gamma-ray bursts (GRBs) in near real time in the 4-150 keV energy band. The design of ECLAIRs has been mainly driven by the objective of achieving a low-energy threshold of 4 keV, unprecedented for this type of instrument. The detection plane is an assembly of 6400 Schottky CdTe semiconductor detectors of size 4x4x1 mm 3 organized on elementary hybrid matrices of 4x8 detectors. The detectors will be polarized from -300V to -500V and operated at -20°C to reduce both the leakage current and the polarization effect induced by the Schottky contact. The remarkable low-energy threshold homogeneity required for the detection plane has been achieved thanks to: i) an extensive characterization and selection of the detectors, ii) the development of a specific low-noise 32-channel ASIC, iii) the realization of an innovative hybrid module composed of a thick film ceramic (holding 32 CdTe detectors with their high voltage grid), associated to an HTCC ceramic (housing the ASIC chip within an hermetic enclosure). In this paper, we start describing a complete hybrid matrix, and then the manufacturing of a first set of 50 matrices (representing 1600 detectors, i.e. a quarter of ECLAIRs detector’s array). We show how this manufacturing allowed to validate the different technologies used for this hybridization, as well as the industrialization processes. During this phase, we systematically measured the leakage current on Detector Ceramics after an outgassing, and the Equivalent Noise Charge (ENC) for each of the 32 channels on ASIC Ceramics, in order to optimize the coupling of the two ceramics. Finally, we performed on each hybrid module, spectral measurements at -20°C in our vacuum chamber, using several calibrated radioactive sources ( 241 Am and 55 Fe), to check the performance homogeneity of the 50 modules. The results demonstrated that the 32-detector hybrid matrices presented homogeneous spectral properties and that a lowenergy threshold of 4 keV for each detector could be reached. In conclusion, our hybrid module has obtained the performance required at the SVOM mission level and successfully withstood the space environment tests (TRL 6/7). This development phase has given us the opportunity to build a detector’s array prototype (Engineering Model) equipped with 50 hybrid modules. Thanks to this prototype we are in the process of validating a complete detection chain (from the detectors to the backend electronics) and checking the performance. In addition it enables us to consolidate the instrument’s mechanical and thermal design, and to write preliminary versions of the quality procedures required for integration, functional tests and calibration steps. At the end of this prototype development and testing, we will be ready to start the detailed design of the detection plane Flight Model.

The Microchannel X-Ray Telescope will be implemented on board the SVOM space mission to observe the afterglow of gamma-ray bursts and localize them with 2 arcmin precision. The optical system is based on microchannel plates assembling in Wolter-I configuration to focus the X-rays in the focal plane, like done for the MIXS telescope of the BepiColombo ESA mission. The sensor part is a 256 × 256 pixel pnCCD from the Max-Planck Institute for Extraterrestrial Physics for high resolution spectroscopy and high quantum efficiency over 0.2 – 10 keV energy range, based on the same technology and design as the eROSITA telescopes for the Russian-German SRG mission. CEA-Irfu (Saclay) is in charge of the design and the realization of the camera, including the focal plane, the calibration wheel, the front-end electronics, the structure housing for background shielding and the active cooling system. A prototype of the full detection chain and the acquisition system was set up. The paper presents the preliminary design of the electrical, mechanical and thermal architectures of the camera. It focuses on the fabrication and testing of the critical elements of the design and concludes on the on-going developments.

The SVOM (Space-based multi-band astronomical Variable Objects Monitor) French-Chinese mission is dedicated to the detection, localization and study of Gamma Ray Bursts (GRBs) and other high-energy transient phenomena. We first present the major principles of the SVOM system including the alert system providing near-real-time GRB localizations to large ground-based telescopes. Then the paper describes the definition of the SVOM payload and more particularly the French payload composed of the ECLAIRs instrument, dedicated to GRB detection and positioning, and the MXT instrument, dedicated to GRB followup observation in soft X-ray band.