In-orbit operation and spectrum analysis of the GRID-02 CubeSat detector

The Gamma-Ray Integrated Detectors (GRID) mission is a space science project that uses multiple CubeSats carrying scintillation detector payloads based on silicon photomultipliers (SiPMs) to detect gamma-ray bursts (GRBs) associated with high-energy astrophysical transients. In this paper, we present the in-orbit observation strategy and spectrum analysis of GRID-02, the second detector of GRID mission, and verify the working status of the detector. We set bias voltages of SiPMs to a constant value and record necessary housekeeping data during the detector's operation in order to correct the signal amplitudes to a standard condition. We use both the on-ground calibration results and in-orbit data to reconstruct detected energies from original data. We analyze the spectrum of GRB 210121A observed by GRID-02 with the response matrix generated from Monte Carlo simulation, and the fitting result is consistent with the joint analysis result of other instruments including Fermi/GBM, HXMT and GECAM. This result proves that GRID-02 detector performs well and that GRID can produce valuable data for high-energy astrophysical transients' research.