|AHELP for CIAO 4.9 Sherpa v1||
Decay in the ACIS quantum efficiency. XSPEC model.
Users should be aware of the following before including this model in their analysis.
- Since 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- This model is out of date since it doesn't include any spatial variation and includes an early version of the spatially-invariant model.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.
This is a multiplicative model component.
|1||tdays||Days between Chandra launch and ACIS observation|
|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 12.9.0o of the XSPEC models is supplied with CIAO 4.9.
For a list of known bugs and issues with the XSPEC models, please visit the XSPEC bugs page.
To check the X-Spec version used by Sherpa, use the get_xsversion routine from the xspec module:
sherpa> from sherpa.astro.xspec import get_xsversion sherpa> get_xsversion() '12.9.0o'
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