A next-generation medium-energy (100 keV to 100 MeV) gamma-ray observatory will greatly enhance the identification and characterization of multimessenger sources in the coming decade. Coupling gamma-ray spectroscopy, imaging, and polarization to neutrino and gravitational wave detections will develop our understanding of various astrophysical phenomena including compact object mergers, supernovae remnants, active galactic nuclei and gamma-ray bursts. An observatory operating in the MeV energy regime requires technologies that are capable of measuring Compton scattered photons and photons interacting via pair production. AstroPix is a monolithic high voltage CMOS active pixel sensor which enables future gamma-ray telescopes in this energy range. AstroPix’s design is iterating towards low-power (∼1.5mW/cm2), high spatial (500 μm pixel pitch) and spectral (<5 keV at 122 keV) tracking of photon and charged particle interactions. Stacking planar arrays of AstroPix sensors in three dimensions creates an instrument capable of reconstructing the trajectories and energies of incident gamma rays over large fields of view. A prototype multi-layered AstroPix instrument, called the AstroPix Sounding rocket Technology demonstration Payload (A-STEP), will test three layers of AstroPix “quad chips” in a suborbital rocket flight. These quad chips (2×2 joined AstroPix sensors) form the 4×4 cm2 building block of future large area AstroPix instruments, such as ComPair-2 and AMEGO-X. This payload will be the first demonstration of AstroPix detectors operated in a space environment and will demonstrate the technology’s readiness for future astrophysical and nuclear physics applications. In this work, we overview the design and state of development of the A-STEP payload.
The precise reconstruction of Compton-scatter events is paramount for an imaging medium-energy gamma-ray telescope. The proposed AMEGO-X is enabled by a silicon tracker utilizing AstroPix chips - a pixelated silicon HVCMOS sensor novel for space use. To achieve science goals, each 500 × 500 μm2 pixel must be sensitive for energy deposits ranging from 25 - 700 keV with an energy resolution of 5 keV at 122 keV (< 10%). This is achieved through depletion of the 500 μm thick sensor, although complete depletion poses an engineering and design challenge. This talk will summarize the current status of depletion measurements highlighting direct measurement with TCT laser scanning and the agreement with simulation. Future plans for further testing will also be identified.
All-sky medium-energy gamma-ray observations are essential to deepen our understanding of physics in high energy astronomical phenomena, and to further develop multi-messenger astronomy. Future all-sky MeV gamma-ray telescopes must have a large area detector and keep high sensitivities even in the energies in which Compton scattering is dominant. AMEGO-X is one of the proposed MeV gamma-ray missions and its gamma-ray detector consists of silicon trackers and calorimeters. In order to efficiently detect MeV photons and to have precise Compton reconstruction, the silicon sensors must be fully depleted (500 μm) and have a moderate position resolution (∼ 500 μm) with a good energy resolution (< 10% at 60 keV). On top of that, the power consumption of the silicon detector must be low (< 1.5 mW/cm2) given the required silicon area in the gamma-ray detector is huge (∼ 24 m2). We have been developing AstroPix, a high-voltage CMOS active pixel sensor, to fulfill such specifications. In this contribution, we report basic characterization of the third version of AstroPix chip (AstroPix3), such as I-V measurement, imaging capability, energy spectrum, and indirect depletion depth measurements using gamma-ray sources.
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