A stepwise calculation method of response matrix for GRID constellation

Abstract The Gamma-Ray Integrated Detectors (GRID) mission is designed to monitor transient gamma-ray phenomena using compact gamma-ray detectors mounted on NanoSats in low Earth orbit (LEO). Currently, the GRID constellation, comprising tens of detectors, is under development to establish a full-time, all-sky monitoring network in the future. In the GRID constellation, the response of each detector is determined solely by its own characteristics. Identical responses are shared among detectors of the same type, where the photon response within a satellite varies for each payload, depending on the satellite's structural configuration. Leveraging this characteristic, a stepwise calculation method is proposed to independently handle two distinct types of responses, with a coupling algorithm employed to compute the final response matrix. The response matrices derived from this stepwise approach show consistency with direct Monte Carlo simulations. At the test grid points, 79% of energy bins exhibit relative deviations within 10%. The larger deviations observed in certain energy bins are primarily caused by the current calculation method's inability to adequately describe multiple interactions of high-energy incident photons. This method provides a more adaptable framework for generating response matrices and improves data management in simulation analysis and processing for the GRID constellation.