The point spread function of the soft X-ray telescope aboard Yohkoh |
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| Authors: | Petrus C Martens Loren W Acton James R Lemen |
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| Institution: | (1) Space Science Department, ESA/ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands;(2) Department of Physics, Montana State University, 59717 Bozeman, MT, USA;(3) Lockheed Palo Alto Research Laboratory, 3251 Hanover Street, 94304-1121 Palo Alto, CA, USA |
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| Abstract: | The point spread function of the SXT telescope aboardYohkoh has been measured in flight configuration in three different X-ray lines at White Sands Missile Range. We have fitted these data with an elliptical generalization of the Moffat function. Our fitting method consists of  2 minimizationin Fourier space, especially designed for matching of sharply peaked functions. We find excellent fits with a reduced 2 of order unity or less for single exposure point spread functions over most of the CCD. Near the edges of the CCD the fits are less accurate due to vignetting. From fitting results with summation of multiple exposures we find a systematic error in the fitting function of the order of 3% near the peak of the point spread function, which is close to the photon noise for typical SXT images in orbit. We find that the full width to half maximum and fitting parameters vary significantly with CCD location. However, we also find that point spread functions measured at the same location are consistent to one another within the limit determined by photon noise. A  best analytical fit to the PSF as function of position on the CCD is derived for use in SXT image enhancement routines. As an aside result we have found that SXT can determine the location of point sources to about a quarter of a 2.54 arc sec pixel.This paper is dedicated to the memory of our friend and colleague Kermit Smith, who died in June 1993, after a valient fight with leukemia. |
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