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Line Spread Function

We use the term Line Spread Function (LSF) to describe the redistribution of photons from a source which is a delta function, spectrally and spatially, and integrated in either the dispersion or cross-dispersion direction. The product caclulated here is from the HRMA and the gratings but does not currently include aspect or processing effects. The integration region is $\pm$ 5.3 $^{\prime\prime}$ for the dispersion and cross-dispersion data which includes most of the power in the line. A few tenths of a percent of the total number of photons are scattered outside this integration region.

In flight the spectra of celestial sources has contributions from several sources which affect the LSF. The most important is the blurring introduced by the mirror (the HRMA PSF) and is discussed in Calibration Document TBD. The HRMA PSF is further blurred by the redistribution from the transmission gratings. Additional blurring is introduced from errors in the aspect solution and pixelization of the detector.

David Davis