Kurzbeschreibung
(Englisch)
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Silicon Photomultiplier (SiPM) technology for photon detection is playing an increasingly important role in astrophysics X-ray and gamma-ray space missions to detect weak transients and alert the community with spectral and localization information, which is a key ingredient in the field of multi-messenger and time-domain astrophysics.
Traditional gamma-ray detectors are based on scintillators read out by Photo-Multiplier Tubes (PMT) which are relatively bulky and require to be operated at kV level voltages. SiPMs, on the other hand, are more compact and require typical operating voltages below 100 V. These properties make SiPMs ideal for replacing PMTs, especially for compact small-scale space-based detectors.
Within the POLAR-2 [1] gamma-ray polarimeter project, the UniGe group has developed a compact and low-power Front-End readout Electronics (FEE) that allows to read out 64 SiPM channels. The design of the POLAR-2 FEE [2] is flexible, allowing it to be adopted to read out different types of detectors and SiPMs. Currently, it has been adopted, in addition to the POALR-2 polarimeter, by the sister payload of POLAR-2, the Broad Spectrum Detector (BSD), as well as by the future X-ray observatory eXTP mission [3] for its wide field transient monitor (W2C). It has also been adopted by the cosmic X-ray background instrument CXBe [4] which is under study with NASO support.
Very recently a project to flight-test the POLAR-2 FEE with 2 BSD modules on board the “Guizhou Normal University Science Satellite No. 1” (GNU-1) has been developed. GNU-1 is an experimental microsatellite project led by Guizhou Normal University in collaboration with the Institute of High Energy Physics of Chinese Academy of Sciences (IHEP) and other partners. This project will deploy two detector modules developed by IHEP based on the POLAR-2 Broad-band Spectrometer Detector (BSD) design, using the POLAR-2 FEE developed by UniGe. Besides the in-orbit characterization of the POLAR-2 FEE and the BSD module, it will conduct space X-ray astronomical observations that can yield significant scientific insights into high-energy celestial events such as magnetars and Gamma-Ray Bursts (GRBs). This microsatellite is scheduled for launch in mid-2026, ahead of POLAR-2, which is expected to launch around mid-2027.
This test is necessary and useful because it allows to qualify the POLAR-2 FEE in-flight, to gain long-term operational experience, and to characterize it with actual scientific observations, thus bringing it to TRL 9. This test was not foreseen as part of POLAR-2 since flight-test opportunities are extremely rare.
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