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ACIS Calibration Issues in Progress

Last updated: 08/02/2001

                Richard J. Edgar
                edgar@head-cfa.harvard.edu

Previous editions:
ACIS-Cal-Progress-010112.html - 01/12/2001


The response of the Back Illuminated (BI) chips is being reworked.

The January 2000 (CALDB 2.0) release of the BI matrices has systematic problems with its energy scale and line widths. See discussions here for the energy scale, and here for the line widths.

Quantum Efficiency. There is some evidence (ref: Herman Marshall's page http://space.mit.edu/ASC/calib/letg_acis/ck_cal.html) that the S3/S2 sensitivity ratio is larger than we have advertised by 10-20% in the energy regime below 1 or 1.2 keV. We are investigating this by several methods, including flight grating spectra of multiple AGN and QSO targets, re-analysis of low-energy ground calibration data, and fitting of spectra from other flight targets (notably hot clusters of galaxies). It's difficult to disentangle this effect from the (to date poorly modelled) asymmetries in the line shape function at low energies. Re-analysis of ground calibration data will be required to decide which (if either) of the QE curves is the correct one. This is an ongoing topic of debate within the calibration group and the PI team, and may not be resolved until late 2001 (or later).

Front Illuminated (FI) chip response, and CTI correction

Also in work:

Here are the viewgraphs presented to the Chandra Users' Committee on 2001-JUN-29. http:CUC_2001_06_29.ps

Last revised: Thu Aug 2 10:29:02 EDT 2001