A simulation result of X-ray focusing mirror under actual surface state used in FXT on board EP satellite

The Follow-up X-ray Telescope (FXT) is one of the main payloads on board the Einstein probe satellite. In order to obtain data with high signal-to-noise ratio and realize high-precision positioning of the sources, FXT adopts Wolter-I X-ray focusing optical system which has been wildly used in X-ray astronomy. According to the principle of Wolter-I, combined with the actual manufacture characteristics, several key parameters affecting the optical quality, such as surface roughness Root-Mean Square (RMS) and surface profile error, are simulated by Monte Carlo simulation algorithm. The effect of each parameter is analyzed according to the simulation results. Then, the simulation method is verified by the test results of the focusing mirrors provided by PANTER laboratory, and the surface profile error parameters are restricted. The simulation results of the Half Energy Width (HEW) of the Structural-Thermal Module mirrors are basically consistent with the test results. This method can be effectively applied to later study of focusing mirrors manufacture and to accumulate experience for test and calibration work of FXT focusing mirrors. Furthermore, combined with the tested calibration data, some key performance of the mirrors such as the effective area, vignetting and the point spread function which can compose the on-orbit calibration database can be obtained by this simulation method.