The THESEUS mission and the XGIS instrument: verification of the scientific requirements with testing of the first ORION front-end electronics prototypes

The Transient High-Energy Sky and Early Universe Surveyor, THESEUS, is a proposed space mission developed by a large European collaboration, submitted in 2016 to the European Space Agency (ESA). In 2018, THESEUS, along with other two mission concepts, was selected by ESA for a 3-year Phase A assessment study, but in 2021 it was not selected for launch. However, THESEUS has been re-proposed in 2022 for the M7 call. Currently, it has just concluded the preliminary phase 0, which included the CDF, and is pending for the ESA decision for admission to the next phases of the selection. THESEUS will provide a wide and deep sky monitoring in a very broad energy band (0.3 keV – 10 MeV), focusing capabilities in the soft X-ray band, large grasp and high positional accuracy, with on board near-IR capabilities for immediate transient identification, arcsecond localization, and redshift determination; furthermore, it will provide a high-degree of spacecraft autonomy and agility, along with the capability of promptly transmitting to ground transient trigger information. The instruments onboard THESEUS are XGIS, a set of two coded-mask monitor cameras using monolithic SDD and CsI(Tl) scintillator-based X-ray and gamma-ray detectors dedicated to the detection of Gamma-ray bursts (GRB), performing imaging up to 150 keV and spectroscopy up to 10 MeV; SXI, two lobster-eye monitors dedicated to the follow-up in soft X-ray and imaging after the detection of XGIS; and IRT with imaging and spectroscopy capabilities dedicated to the follow-up in the infrared waveband and the measure of the redshift of the GRB. In this thesis we characterized the first prototypes of the ORION ASIC, a multi-chip readout circuit designed for XGIS. In particular my work concerns the characterization of two detector prototypes with ORION, to test if they are compliant with the official ESA requirements; these prototypes are thought to maximize the scientific production of the XGIS detector.