ACIS Instrument Support - Monthly Progress Report for April 2000


1. ACIS Characterization

1.1 Characterize and model radiation damage in ACIS CCDs

  ... Continued effort to model the volume occupied by a charge packet as a function of signal charge in the CCD pixels.  The flight software CTI corrector requires this relationship for accurate results.

1.2 Define and characterize alternative CCD readout modes

 [...  Conducted tests of squeegee readout mode on flight device S0.

       * 07 April - ran 16-row squeegee mode.  Clock sequences were not optimized but efficacy of squeegee still apparent.

       * 15 April - ran 16-row and 8-row squeegee mode.  Both tests show improvement in the CTI and FWHM over normal clocking.  Excess charge is present in the bias level that decays during the observations.  (ACIS Memos #183, 184, 185; available at http://space.mit.edu/ACIS/iacis.html)

       * Prepared for 02 May test of 16-row squeegee mode in raw frame mode to study time-dependence of bias level.

  ...  Continued lab testing of squeegee readout mode using w459c1.

       * Tested slow parallel transfer squeegee readout.  Produced a modest decrease in the FWHM. Effect is enhanced if the slow transfer is applied to the forward parallel clocking instead of the reverse clocking as is the current case. Indicates that the previously reported decreases in FWHM were due to enhanced charge recapture. Using the slow parallel clocking on the reverse transfer only did not reproduce the earlier result.

       * Tested subarray readout with squeegee.  As expected, subaray readout of the top (128, 256, 384, 512) rows with squeegee did produce the smallest FWHM. Suggests that observations of small sources in the focal sweet-spot could benefit from this readout method.

  [...] tested squeegee readout mode in lab on BI device w147c3.  No change measured.

1.3 Monitor scientific on-orbit performance of ACIS

  ... Continued monitoring of ACIS CTI.  Investigated possible degradation associated with CME around 06 April.  Investigation ongoing however any increase in CTI would have to be quite small (<< 10^-6).  No additional radiation damage detected for BI CCDs.  

1.4 Update and improve CCD simulation

 [...] Prepared new QE curves with higher energy resolution for submission to CXC Calibration Group.  Higher energy resolution QE data across absorption edges required for accurate gratings data analysis.


2. Engineering

2.1 Flight software maintenance

2.2 Instrument science performance

  ...  Continued quick-look processing of all ACIS science runs, using EHS telemetry supplied by the GOT.

  ...  Continued to publish the "annotated DOT" timeline reports.

  ...  Monitored performance of new ACIS Flight Software patches including FEP bias parity error fix.  FEP bias parity errors never exceeded trigger value.

2.5 Participate in Chandra activities

 [...] Supported squeegee readout mode tests on 07 April and 15 April including load and CAP review and real-time data analysis support.


3. CXC Support

3.1 Provide user support

  ...  Continued to assist the CXC MTA in CTI monitoring and background correlations.

  ...  Supported discussions of radiation damage limits from bright X-ray sources.

  ...  Updated ACIS memo listing calibration ObsIDs and observation characteristics (ACIS Memo #165).


4. OCC Support

4.1 Use of MIT/ACIS EGSE at OCC

  ...  Continued support and maintenance of ACIS EGSE software at the OCC.