Optical Performance Simulation and Analysis of the Spectroscopy Focusing Array-Timing (SFA-T) X-Ray Telescope onboard the enhanced X-Ray Timing and Polarimetry (eXTP)

Abstract The Spectroscopy Focusing Array-Timing (SFA-T) constitutes a principal payload onboard China’s enhanced X-ray Timing and Polarimetry mission (eXTP). To achieve substantial effective area, optimize observational efficiency, and maintain high-precision positioning capabilities, the eXTP mission employs fifty nested Wolter-I mirror shells as its optical architecture across all payloads. Although payload-specific variations exist in coating selection and manufacturing specifications due to differing energy ranges and angular resolution requirements, the fundamental geometric design parameters remain consistent throughout the system. This study presents comprehensive optical simulations of the SFA-T system, which comprises five identical telescope modules. The optical configuration achieves an effective area of 910 cm 2 at 1.50 keV with angular resolution characterized by HPD = 1 ′ and W90 = 3 ′ . Simulations reveal a field of view measuring 18. 4 ′ × 17. 2 ′ and demonstrate that stray light contributes merely 0.1% to central pixel contamination in multi-pixel Silicon Drift Detector, thereby eliminating the requirement for external X-ray baffles. Ground calibration measurements exhibit 29%–43% effective area reduction relative to on-orbit performance due to beam divergence effects. The integrated five-telescope configuration satisfies design specifications for effective area, thereby validating the optical performance for high-precision X-ray timing observations. Furthermore, all these simulation results will play an indispensable role in the calibration implementation and in establishing the on-orbit calibration database for the SFA-T.