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Decay in the ACIS quantum efficiency.
XSpec model.
Users should be aware of the following before including this model
in their analysis.
-
As of CIAO 3.0, the ACIS QE degradation is accounted for when
response files are created. This model is no longer needed if you
are using that version (or newer) of the software.
-
This model is out of date since it doesn't include any spatial
variation and includes an early version of the spatially-invariant
model.
This model accounts for the decay in the ACIS quantum efficiency most
likely caused by molecular contamination of the ACIS filters. The user
needs to supply the number of days between Chandra launch and
observation. The xsacisabs parameters related to the composition of the
hydrocarbon and the rate of decay should be frozen and not
modified. The present version of xsacisabs is to be used for the
analysis of bare ACIS I and ACIS S data. For the present version of
xsacisabs one must use the standard QE file vN0003 instead of the
optional vN0004 file.
Because of the present large uncertainity in the ACIS gain at energies
below 350eV we recommend that events in the 0-350eV range be ignored
in the spectral analysis until the gain issue is resolved.
xsacisabs calculates the mass absorption coefficients of the
contaminant from atomic scattering factor files.
xsacisabs Parameters
| 1 | Tdays |
Days between Chandra launch and ACIS observation |
| 2 | norm |
normalization factor |
| 3 | tauinf |
Slope of linear quantum efficiency decay |
| 4 | tefold |
Offset of linear quantum efficiency decay |
| 5 | nC |
Number of carbon atoms in hydrocarbon |
| 6 | nH |
Number of hydrogen atoms in hydrocarbon |
| 7 | nO |
Number of oxygen atoms in hydrocarbon |
| 8 | nN |
Number of nitrogen atoms in hydrocarbon |
This information is taken from the XSpec User's Guide. Version 11.3.1 of the XSpec
models is supplied with CIAO 3.2.
For a list of known bugs and issues with the XSPEC models, please visit the XSPEC bugs page.
- sherpa
-
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- slang
-
usermodel
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