Simulation study of the performance of the Very Large Area gamma-ray Space Telescope

The Very Large Area gamma-ray Space Telescope (VLAST) is a mission concept proposed to detect gamma-ray photons through both Compton scattering and electron–positron pair production mechanisms, thus enabling the detection of photons with energies ranging from MeV to TeV. This project aims to conduct a comprehensive survey of the gamma-ray sky from a low-Earth orbit using an anti-coincidence detector, a tracker detector that also serves as a low-energy calorimeter, and a high-energy imaging calorimeter. We developed a Monte Carlo simulation application of the detector using the GEANT4 toolkit to evaluate the instrument performance, including the effective area, angular resolution, and energy resolution, and explored specific optimizations of the detector configuration. Our simulation-based analysis indicates that the current design of the VLAST is physically feasible, with an acceptance above 10 \(\mathrm m^2\, \text{sr}\) which is four times larger than that of the Fermi-LAT, an energy resolution better than 2% at 10 GeV, and an angular resolution better than 0.2\(^\circ\) at 10 GeV. The VLAST project promises to make significant contributions to the field of gamma-ray astronomy and enhance our understanding of the cosmos.