Abstract
The Gamma-ray Transient Monitor(GTM)is an all-sky monitor onboard the Distant Retrograde Orbit-A(DRO-A)satellite with the scientific objective of detecting gamma-ray transients ranging from 20 keV to 1 MeV.The GTM was equipped with five Gamma-ray Transient Probe(GTP)detector modules utilizing a NaI(Tl)scintillator coupled with a SiPM array.To reduce the SiPM noise,GTP uses a dedicated dual-channel coincident readout design.In this work,we first studied the impact of dif-ferent coincidence times on the detection efficiency and ultimately selected a 0.5 μs time coincidence window for offline data processing.To test the performance of the GTPs and validate the Monte-Carlo-simulated energy response,we conducted compre-hensive ground calibration tests using the Hard X-ray Calibration Facility(HXCF)and radioactive sources,including the energy response,detection efficiency,spatial response,bias-voltage response,and temperature dependence.We extensively present the ground calibration results and validate the design and mass model of the GTP detector,thus providing the foundation for in-flight observations and scientific data analysis.
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