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Total Spectral Response Effective Area

    

There are now three sets of official total effective areas which have been distributed by SASS. Just to be clear, the total effective area files contain:

1. the on-axis mirror effective area
2. the mirror vignetting function
3. the window transmission (including the average transmission of the wire mesh)
4. the gas absorption function

with only the window transmission changing between the three datasets.   However, it is planned to update the gas absorption function to include effects (different path lengths in the active regions) due to the bulge in the PSPC window due to gas pressure (which is likely to amount to few percent changes in the total effective area above 2 keV).

It should be noted that up until the latest datasets (SASS_AREA_B_NEW2 and *._C_NEW2), rigorous checks were not made that all components were included correctly. The 1st datasets (SASS_AREA_B etc.) are likely to have a errors at low energies. Based on high gain HZ43 observations, the polypropylene thickness (within the window) was reduced by to produce SASS_AREA_C_NEW1. Unfortunately there was a low energy problem in these data. The SASS_AREA_B_NEW2 and *._C_NEW2 files were adjusted for PI < 10 to reduce this low energy problem. There is also a few percent change at the C edge, cf. SASS_AREA_B_NEW1 etc. (which had gone unnoticed); see Chap. G.

It should be noted that the detector maps do show variations at the few percent level on scales of tens of arc minutes.  This is consistent with window thickness variations at fabrication. The 0.25 keV map may also have a top-bottom (in detector coordinates) gradient at a similar level. Furthermore, some ablation is possible within the central, most-used region of the detector. Currently however, it is not intended to fold these effects into the effective area datasets, although the effects are under confirmation/investigation.