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| Product | Status | Accuracy |
|---|---|---|
| LETG/HRC-S effective area | Updated 7/02 | 15% over whole range. Much improved edge structure. |
|
LETG efficiency (m=0,1,3) | Updated 3/00 | 10% -- 3rd/1st relative efficiency confirmed 8/04 |
|
LETG efficiency (m=2,4,5,6,7) |
Updated 8/04 in CALDB 2.28 | 10% relative to 1st order, 15% absolute. Incorporated new ACIS-S1 and S3 QEs. Minor changes for odd orders. 2nd order changes were the largest (-40% to +65%). |
| Bowtie spectral extraction region |
Completed 4/00, bug fixed 6/01 |
Spectral extraction efficiency accurate to 2% |
| HRC-S Degap Map | Updated 6/01 | Typically 1-2 pixels (0.007 Å), but with some deviations of 5-10 pixels. An update (ps) is under development. |
| Dispersion relation | Updated 7/00 | RMS 0.014 Å, but with some localized displacements of 5-10 pixels (0.037-0.074 Å). Efforts to improve this are ongoing. |
| Line Spread Function (RMFs) | Updated 5/01 | ACIS/LETG: OK for Sherpa, 1st order only HRC-S/LETG: Orders 1-6, OK for proposals, but not yet good enough for Sherpa |
| HRC-S gain map | Updated 11/08 | Relative accuracy of 2% with 1/3-tap grid (0.63 Å without dither), but somewhat worse near the optical axis and plate ends. This new gain map is time dependent and permits much more effective background filtering than the 2001 gain map and filter, but users will have to reprocess their data using contributed software. Implementation in CIAO/CALDB is expected sometime in 2009. |
| HRC-S/LETG
background filter |
Updated 11/08 | This filter is used in conjunction with the new time-dependent gain map and removes more than half of the L2 background at most wavelengths with a 1.25% loss of 1st order X-ray events. The new filter is much more effective than the old filter, particularly for recent observations, but users will have to reprocess their data using contributed software. Implementation in CIAO/CALDB is expected sometime in 2009. |
The LETG/HRC-S effective area (for both on-axis and off-axis sources) incorporates the LETG diffraction efficiency, HRC-S QE, and extraction region efficiency. This is what observers should use when analyzing spectra.
The new HRC-S gain map and LETG/HRC-S background filter will be incorporated into CIAO/CALDB sometime in 2009.
The gain of the HRC (both S and I) is very slowly decreasing, but so far this has had no effect on detector QE. An unrelated wavelength-independent gradual decrease in HRC-S QE, currently (2008) about 5% since launch, is being monitored.
Now that data have been reprocessed using the new degap map, we are recalibrating the line spread function (LSF) and dispersion relation. With the new degap map, gaps between taps are typically one pixel or less, which should improve dispersion linearity. Even so, systematic wavelength residuals on the outer two HRC-S segments will probably remain, and so we will make ad hoc corrections for the next dispersion relation update, bringing the overall accuracy close to the 0.01% level.
An update to the degap map that accounts for much of the residual systematic deviations has been constructed, and is being tested. See Kashyap et al., 2004, SPIE 5488-62 (ps) for a preliminary report.
Further improvements in HRC-S performance (such as position accuracy
and background rejection) now hinge on finding ways
to correct or otherwise deal with
x-ray events that yield incorrect pulse-height signals.
This is only a very small fraction (couple percent) of events,
but they are not uniformly distributed over the detector, so
localized errors can be significant if we apply adjustments
or filters too aggressively.
Last modified: 11/21/08
 |
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