Jeremy Drake writes (9/4/96):The HSI event map for the HEG Herman scattering test looks a bit like the following, where the dots represent photon events:-
. :: . :::: .:::: / \:. / \ . / \ . <---mysterious weak scattered light along dispersion axis / \ (at angle of ~5 deg to "horizontal") HSI mask occulting cusp
This was taken with the DCM tuned to catch the W 1.775 keV line which was carefully positioned over the "cusp" of the HSI mask (to avoid overexposure of the line core), and then a similar exposure taken with the DCM de-tuned to 1.76 keV - off the energy of the line. In the de-tuned image, the scattering is not present. Scattering (possible broad, shallow wings of instrumental profile) in the DCM itself is not likely because the de-tuned image does not show the scattering. Not to panic though: if we do rough back-of-the IDL envelope calculations of the total flux in the scattered spectrum it looks like ~0.5% (less than 1%, probably slightly more than 0.1%) of the line flux.