Optimization of CdZnTe low energy threshold utilizing readout ASIC charge pumping for the High-Resolution Energetic X-ray Imager SmallSat Explorer

The High-Resolution Energetic X-ray Imager SmallSat Explorer (HSE) is a proposed wide-field, hard X-ray (3-300 keV) coded aperture telescope. Operating a closely tiled array of pixelated CdZnTe (CZT) detectors, HSE seeks to rapidly localize short gamma ray bursts (GRBs) resulting from neutron star and black hole mergers and search for faint undiscovered black hole low mass x-ray binaries. The spectral signatures of these phenomena fall off as a power law, thereby motivating the improvement of HSE’s hard x-ray band coverage at lower energies. This is achievable by tuning HSE’s Nuclear Spectroscopic Telescope Array (NuSTAR) ASIC detector readout and operating in a charge pumping mode. This can extend energy band coverage to as low as 2-3 keV, but requires careful independent tuning of each of the instrument’s ASIC devices. An optimization procedure for efficiently tuning the detector readout via commandable ASIC registers is reported.