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Paper: Cosmic Ray Identification and Ramp-fitting in JWST Data
Volume: 461, Astronomical Data Analysis Software and Systems XXI
Page: 785
Authors: Grumm, D.; Greenfield, P.
Abstract: Cosmic rays are expected to significantly affect on-orbit JWST detectors as the cosmic-ray environment does not benefit from shielding by the Earth's magnetic field. Data is read non-destructively (up-the-ramp) so cosmic rays can be recognized as jumps in the pixel ramps as signal accumulates. Because the effect of a cosmic ray is to add a large and unpredictable number of counts to the signal, it is important to correctly flag cosmic rays to enable valid count rates to be calculated for science pixel data. Once the cosmic rays are identified, a fit can be performed for the data between cosmic ray-affected reads, allowing the count rate for each pixel to be estimated. In lieu of having on-orbit data on which to test cosmic ray rejection algorithms and fitting algorithms, a set of Python scripts was written to generate artificial datasets that include realistic celestial sources and cosmic rays. An investigation was made into ways of detecting cosmic rays, and then how to measure the underlying count rate signal in the presence of these jumps. As the on-orbit datasets will be large, techniques to reduce the processing time by reducing the memory requirements and reordering the data have been investigated. Cosmic ray rejection and ramp fitting will be incorporated into the JWST Calibration pipeline to reduce on-orbit data.
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