ACIS Instrument Support - Monthly Progress Report for April 2007

1.  ACIS Characterization

1.1 Characterize and model radiation damage in ACIS CCDs

  ...  Continued work on a paper presenting the results of
the radiation damage/reverse annealing tests done at GSFC in 2005.

1.3 Monitor scientific on-orbit performance of ACIS

  ...  Continued investigation of bias artifacts believed to be
due to long-lived cosmic ray afterglows.  Created "superbiases",
bias maps created from tens to hundreds of biases which removes
the transient bias artifacts.  Evaluating stability of superbiases
for possible use in ground processing.

  ...  Continued monitoring of ACIS CTI, gain, trailing pixel 
pulseheight, detector efficiency, corner pixel distribution, and 
spectral line centroid and width.  Updated monitoring web pages.
(http://space.mit.edu/~cgrant/monitor.html)

  ...  Updated monitoring web pages to reflect new temperature
filters.  The allowed temperatures now better reflect the
intrinsic temperature dependence of the data.  In most cases this
increases the number of data points.

  ...  Re-analyzed high energy QE monitoring for the BI CCDs.
Now analysis is restricted to low row numbers like the FI CCDs.
This removes an apparent droop in QE with time that is most likely
due to CTI effects.

  ...  Updated contamination monitoring to include measurements at
1.5 keV in addition to the previous 0.7 keV.

  ...  Requested regular monitoring of raw data frames.  These
will be collected a few times a month starting in May.

1.7 Produce novel data products from the MIT ACIS database

  ...  Provided ACIS response team with charge distribution in
each ACIS grade as a function of energy from the subassembly
calibration data.  Work is summarized as a web page and was
presented at ACIS calibration meeting.  This information will
be used in a proposed CTI correction algorithm for graded
mode data.
(http://space.mit.edu/home/fergason/acis/Fcent.html)


2.  Engineering

2.1 Instrument hardware engineering performance

  ...  Continue to monitor long term ACIS instrument performance.
Review of the past 60 days of engineering data indicates no unexpected 
trends.  The instrument continues to perform nominally -- albeit with 
the occasional SEU glitch.

2.2 Flight software maintenance

  ... Developing a new ACIS flight software patch, "buscrash", to
prevent the BEP from crashing when an SCS107 is executed while ACIS
is computing bias maps.  See Software Problem Report 140: "ACIS BEP 
experienced a bus error during SCS107" 
(http://acis.mit.edu/axaf/spr/prob0140.html)

2.3 Instrument science performance

  ...  An ACIS anomaly occured during ObsID 7647 on April 7 when
three FEPs stopped reporting data after first 7 ksec of a 20 ksec
observation.  No error was reported in telemetry and the problem
cleared in the following observation.  Working hypothesis is that
an SEU caused the FEPs to reset.  Investigation ongoing.

  ...  ObsID 7649 on April 28 reported an unusually high number of
bias errors.  Believed to be due to a stuck bit in the bias map.
Error was cleared when FEPs were power-cycled.  Should have no
adverse effect on science data.

  ...  Participated in monthly ACIS operations meeting.  Discussed
ObsID 7647 anomaly, new flight software patch, bias artifacts and
thermal issues.

  ...  Continued daily quick-look processing of ACIS telemetry 
and maintained Web interface to ACIS real-time data.

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


3.  CXC Support

3.1 Provide user support

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

3.2 Provide data analysis support

  ...  Participated in CXC Cal/Ops modeling discussion group.
Presented new contamination monitoring plot which included E0102
OVIII monitoring data provided by Joe dePasquale.  Discussed
graded mode and CC mode calibration and bias artifacts.

  ...  Continued to maintain ACIS calibration database of ground 
and flight data products.


4.  OCC Support

4.1 Use of MIT/ACIS EGSE at OCC

  ...  Continued support and maintenance of ACIS EGSE software 
and hardware at the OCC.  Prepared EGSE for possible real-time 
support during ObsID 7501 - real-time support deemed 
unnecessary.

  ...  Continued work on improving configuration management of 
the ACIS workstations in the TST area of the Chandra OCC.  Work 
nearly complete.


Outreach:

None

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