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Register a new userThe XGIS instrument on-board THESEUS: the detection plane and on-board electronics
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The X and Gamma Imaging Spectrometer instrument on-board the THESEUS mission (selected by ESA in the framework of the Cosmic Vision M5 launch opportunity, currently in phase A) is based on a detection plane composed of several thousands of single active elements. Each element comprises a 4.5x4.5x30 mm 3 CsI(Tl) scintillator bar, optically coupled at both ends to Silicon Drift Detectors (SDDs). The SDDs acts both as photodetectors for the scintillation light and as direct X-ray sensors. In this paper the design of the XGIS detection plane is reviewed, outlining the strategic choices in terms of modularity and redundancy of the system. Results on detector-electronics prototypes are also described. Moreover, the design and development of the low-noise front-end electronics is presented, emphasizing the innovative architectural design based on custom-designed Application-Specific Integrated Circuits (ASICs).
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The XGIS (X and Gamma Imaging Spectrometer) is one of the three instruments onboard the THESEUS mission (ESA M5, currently in Phase-A). Thanks to its wide field of view and good imaging capabilities, it will efficiently detect and localize gamma-ray bursts and other transients in the 2-150 keV sky, and also provide spectroscopy up to 10 MeV. Its current design has been optimized by means of scientific simulations based on a Monte Carlo model of the instrument coupled to a state-of-the-art description of the populations of long and short GRBs extending to high redshifts. We describe the optimization process that led to the current design of the XGIS, based on two identical units with partially overlapping fields of view, and discuss the expected performance of the instrument.
The response of the X and Gamma Imaging Spectrometer (XGIS) instrument onboard the Transient High Energy Sky and Early Universe Surveyor (THESEUS) mission, selected by ESA for an assessment phase in the framework of the Cosmic Vision M5 launch opportunity, has been extensively modeled with a Monte Carlo Geant-4 based software. In this paper, the expected sources of background in the Low Earth Orbit foreseen for THESEUS are described (e.g. diffuse photon backgrounds, cosmic-ray populations, Earth albedo emission) and the simulated on-board background environment and its effects on the instrumental performance is shown.
THESEUS is one of the three missions selected by ESA as fifth medium class mission (M5) candidates in its Cosmic Vision science program, currently under assessment in a phase A study with a planned launch date in 2032. THESEUS is designed to carry on-board two wide and deep sky monitoring instruments for X/gamma-ray transients detection: a wide-field soft X-ray monitor with imaging capability (Soft X-ray Imager, SXI, 0.3 - 5 keV), a hard X-ray, partially-imaging spectroscopic instrument (X and Gamma Imaging Spectrometer, XGIS, 2 keV - 10 MeV), and an optical/near-IR telescope with both imaging and spectroscopic capability (InfraRed Telescope, IRT, 0.7 - 1.8 $mu$m). The spacecraft will be capable of performing fast repointing of the IRT to the error region provided by the monitors, thus allowing it to detect and localize the transient sources down to a few arcsec accuracy, for immediate identification and redshift determination. The prime goal of the XGIS will be to detect transient sources, with monitoring timescales down to milliseconds, both independently of, or following, up SXI detections, and identify the sources performing localisation at < 15 arcmin and characterize them over a broad energy band, thus providing also unique clues to their emission physics. The XGIS system consists of two independent but identical coded mask cameras, arranged to cover 2 steradians . The XGIS will exploit an innovative technology coupling Silicon Drift Detectors (SDD) with crystal scintillator bars and a very low-noise distributed front-end electronics (ORION ASICs), which will produce a position sensitive detection plane, with a large effective area over a huge energy band (from soft X-rays to soft gamma-rays) with timing resolution down to a few $mu$s.Here is presented an overview of the XGIS instrument design, its configuration, and capabilities.
The Infra-Red Telescope (IRT) on board the Transient High Energy Sky and Early Universe Surveyor (THESEUS) ESA M5 candidate mission will play a key role in identifying and characterizing moderate to high redshift Gamma-Ray Bursts afterglows. The IRT is the enabling instrument on board THESEUS for measuring autonomously the redshift of the several hundreds of GRBs detected per year by the Soft X-ray Imager (SXI) and the X- and Gamma-Ray Imaging Spectrometer (XGIS), and thus allowing the big ground based telescopes to be triggered on a redshift pre-selected sample, and finally fulfilling the cosmological goals of the mission. The IRT will be composed by a primary mirror of 0.7 m of diameter coupled to a single camera in a Cassegrain design. It will work in the 0.7-1.8 {mu}m wavelength range, and will provide a 10x10 arc min imaging field of view with sub-arc second localization capabilities, and, at the same time, a 5x5 arc min field of view with moderate (R up to ~500) spectroscopic capabilities. Its sensitivity, mainly limited by the satellite jitter, is adapted to detect all the GRBs, localized by the SXI/XGIS, and to acquire spectra for the majority of them.
The Infra-Red Telescope (IRT) is part of the payload of the THESEUS mission, which is one of the two ESA M5 candidates within the Cosmic Vision program, planned for launch in 2032. The THESEUS payload, composed by two high energy wide field monitors (SXI and XGIS) and a near infra-red telescope (IRT), is optimized to detect, localize and characterize Gamma-Ray Bursts and other high-energy transients. The main goal of the IRT is to identify and precisely localize the NIR counterparts of the high-energy sources and to measure their distance. Here we present the design of the IRT and its expected performance.
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