With the release of CIAO 3.0, the data file can also be used in conjunction with CIAO response generation programs.

The contamination data provided here will work for both grating and imaging use; they were derived specifically from ACIS-S data in conjunction with HETG and LETG. While subject to revision, we anticipate that the current file is close to the final model for ACIS-S, nominal aim point, but there may be revisions for ACIS-I (and eventually we will require spatial dependence).

ISIS is required for ARF-conversion only. The result can be used in any spectral analysis system which supports the ARF format.

ACIS Contamination: General Information

The CXC calibration group's grating scientist for HETGS has provided a preliminary model for the ACIS contaminant which shows edges due to carbon, oxygen, and fluorine. In the model, the depths of these are increasing with time. A CALDB-format data file encodes the absorption as a function of energy and time. When approved, this file (or one with revised content) will become a part of the calibration database (CALDB), and be automatically read by CIAO 3.0 response generation programs (mkgarf, mkarf, mkinstmap).

The model is still under evaluation by the CXC calibration group, and so has not yet been approved for the CALDB. A dummy file has been inserted into the CALDB so CIAO3 response tool defaults will work and produce effective area files which do not account for contamination.

Until release, this page provides resources to incorporate the major features of this effect into your data analysis. Accompanying plots show the magnitude of the effect.

A CIAO 3.0 alternative is to set the ardlib parameter, AXAF_ACIS_CONTAM_FILE to explicitly point at the trial contamination file (instead of CALDB).

Note: The CXC proposal planning suite incorporated the contaminant magnitude as expected in mid-2004.

The contamination data file: --- acisD1999-08-13contamN0001.fits

An ISIS/S-Lang script to apply the contamination to an ARF: --- contamarf

A calibration memo, Measurements of the ACIS Contaminant using the LETG provides a detailed description of the contamination modeling. An older memo is available on the CXC Calibration Group site.