ACIS Instrument Support - Monthly Progress Report for May 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.

 [...] Constructed theoretical understanding of squeegee mode performance.  Using flight and lab data with excess initial charge, extracted more accurate time constants for electron traps.  (ACIS Memo #187) 

1.2 Define and characterize alternative CCD readout modes

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

       * Analyzed initial excess charge and bias decay from Squeegee II test.  Used corner pixel level to remove bias decay (ACIS Memo #185) 

       * 01 May - ran 16-row squeegee mode in raw frame mode (Squeegee III).  Identical time dependence of bias level as seen in previous faint mode test.  Better determined time constants of electron traps (see above).

       * 22 May - ran 16-row squeegee mode with preceding flush frames.  Successfully removed excess intial charge and bias level decay.  (ACIS Memo #186)

 [...  Initiated tests of squeegee mode on flight device I0.

       * 31 May - 16-row squeegee with flush frame.  Identical to 22 May test on S0.  Results as expected.

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

       * Continued exploring new squeegee readout modes.

       * Duplicate excess initial charging seen in flight data.  Developed and tested a fix.

       * Determined that low energy spectral resolution is limited by column to column statistical variation in number of traps, and that these variations appear to be non-varying. This allows for column to column gain correction with the FWHM at oxygen (for example) decreasing to 90 eV from a device average of 130 eV. It has not yet been possible to select columns other than via data intensive x-ray measurement, but it is hoped that some clue in the bias image or the squeegee trailing charge will identify column variations.

       * ACIS Memo #188 summarizes lab squeegee test results

1.3 Monitor scientific on-orbit performance of ACIS

  ...  Continued occasional monitoring of ACIS CTI.  

 [...  Began exploring scripting of xspec to systematically analyze ASC products from external calibration source data

 [...] Found that FI CCD high energy (>3750 ADU) reject rates are related to the depletion depths

1.4 Update and improve CCD simulation

 [...  Began recalibration of S3 QE using sub-assembly and XRCF data and more accurate source/detector models.


2. Engineering

2.1 Flight software maintenance

 [...] Prepared ACIS sequencer loads for continuing squeegee tests

 [...] Developed semi-permanent flight S/W patch for squeegee mode

2.2 Instrument science performance

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

 [...] Rewrote web interface to ACIS pblock, OFLS command file, and OCAT databases

 [...] Developed a plan for hardware upgrade of ACIS engineering unit

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

  ...  Continued development of flight S/W patch to estimate correction for medium time-constant CCD charge traps.

  ...  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 01 May and 22 May 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 and assisted CXC in implementing detrending of CTI data for particle background correction.

  ...  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.


Outreach:

"Chandra X-ray Imaging of Gravitational Lenses", MIT Colloquium, April 25, presented by Mark Bautz

"Chandra and Black Holes", Outreach talk to William S. Diamond Middle School 6th grade science class, May 5, presented by Mark Bautz

Meeting with F. Jansen (XMM PS) at SAO, 2 May, Mark Bautz

New ACIS Memos:

184 - Explanatory note on Squeegee Mode
185 - Analysis of Squeegee Mode Test with Corner-Pixel Bias Correction
184a - Explanatory note on Squeegee Mode (revised)
186 - Preliminary Analysis of Squeegee IV: 16-row squeegee preceded by full frame flush
187 - Squeegee mode; bias stability, trap time constants and related stuff
188 - "Squeegee" Mode Survey on w459c1

all available at http://space.mit.edu/ACIS/iacis.html