The point spread function of the Yohkoh Soft X-ray Telescope

We have analyzed the pre-launch calibration data for characterizing the point spread function (PSF) of the Yohkoh Soft X-Ray Telescope (SXT). Our study shows that both the undersampling effect and the noise in the data should be considered very carefully. The full width at half maximum (FWHM) of the SXT PSF is found to be nearly constant (about one pixel size) over the central area of the CCD where the solar disk is located. The similarity of the results obtained from different wavelengths implies that the contributions from scattering are negligible in the core part of the PSF.