Determination of the point spread function of the Yohkoh Soft X-Ray Telescope Original Research Article

We re-evaluated the point spread function (PSF) of the Yohkoh Soft X-Ray Telescope (SXT). The best-fit model to the ground experimental data can be obtained by considering the undersampling effect at the central area of the PSF. Our result shows that the core of the Moffat function which models the PSF begins to be smoothly connected to the scattering wing at the distance of about 15″ from the peak. Although the available experimental data are limited, first-order vector perturbation theory helps us to consider the wavelength dependence of the scattering wing of the PSF. The autocovariance function of the SXT mirror surface roughness is expressed in our study by the product of exponential function and the modified Bessel function. The calculated angular distribution of the scattering component is compared satisfactorily with the result of in-flight data analysis. The results of the wavelength dependence of the PSF are discussed in detail.