X-GEF Contamination and Effects
X-GEF Contamination and Effects, Version 1.0,
go to HETG Calibration
There is clear data that the SSD and the PSPC windows are very slowly
being coated with a hydrocarbon in the X-GEF vacuum. For the SSD window
this is roughly equivalent to a 1 micron thickness of polyimide
accumulated per year; for the PSPC window the accumulation is of order
0.4 micron of polyimide equivalent per year. This should not to
first-order change the measured grating efficiencies because of the
sample-divided-by-reference measurement technique; however, to a
lesser extent these efficiency changes may influence the fitting process
and resulting measurements.
A clear indication of contamination build-up on the SSD
window is seen in the X-GEF SSD data. Plots over time of the ratio
of SSD count rate to the SMD count rate for X-GEF lines
show a clear trend and energy dependence, Figure cont.1 .
The energy dependence of the change in
the spectral response, Figure cont.2, is reasonably modelled
as a partially covering (60%) of an absorbing layer
(e.g., 3 um of Polyimide accumulated in 2 years).
In comparison, the SMD detector appears stable in response,
Figure cont.3, and can be treated as an accurate measure
of the source spectrum.
- Create a s/w model of the varying SSD window transmission;
compare with data.
- Evaluate the effect of including the SSD contamination in
the SSD X-GEF analysis - how much are results effected? (e.g.,
the zero-order reference grating measurements)
- Determine the dates at which significant SSD and PSPC
"events" took place (warmups, anode changes, window changes);
add these to relevant plots.
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