There has been considerable effort to
develop a software technique to mitigate the charge transfer
inefficiency (CTI) increase caused by radiation-damage to the front-
illuminated chips. Investigation, including in-flight tests, has been
undertaken by the PSU/MIT IPI team, the CXC, and the MSFC Project
Office.
The PSU group has just released an IDL-based empirical correction,
which is now available for users via the contributed software page:
http://asc.harvard.edu/cgi-gen/cont-soft/soft-list.cgi
The CXC is developing code to implement a correction in the CIAO
tools, (and perhaps pipelines). We expect a release in a few months
but work remains to be done specifying the FEFs needed to generate
the new RMF matrices appropriate to CTI-corrected data. The CXC
will also release enhancements to the non-CTI-corrected FEFs
which account for partial-energy-loss tails, and which improve the
fidelity of converting from the measured PHA data to PI energy.
The process of fitting the FEF to our calibration models, and adjusting for
in-flight calibration data, requires several months to complete.
The CXC algorithm to be implemented (see the software spec
at http://space.mit.edu/%egea/docs/memo_cti_correction_4.1.ps) will
follow the PSU empirical correction. It will also incorporate
physical parameters of the degradation as measured by the MIT CCD
group which should improve some of the ad hoc empirical adjustments.
The final CXC results will not be identical to the PSU correction
announced below, but large differences are not expected. We will
compare the two techniques and provide quantitative differences when
the CIAO improvements are ready.
Dan
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Dan Schwartz, MS #3
das@head-cfa.harvard.edu
phone: (617)495-7232 FAX: (617)495-7356
cell phone: (617)512-5627
pager: pager: 877-693 7198 PIN 6937198;
or e-mail 6937198@archwireless.net
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