Detectors for the James Webb Space Telescope Near-Infrared Spectrograph I: Readout Mode, Noise Model, and Calibration Considerations

摘要

We describe how the James Webb Space Telescope (JWST) Near-InfraredSpectrograph's (NIRSpec's) detectors will be read out, and present a model ofhow noise scales with the number of multiple non-destructive readssampling-up-the-ramp. We believe that this noise model, which is validatedusing real and simulated test data, is applicable to most astronomicalnear-infrared instruments. We describe some non-ideal behaviors that have beenobserved in engineering grade NIRSpec detectors, and demonstrate that they areunlikely to affect NIRSpec sensitivity, operations, or calibration. Theseinclude a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using realtest data, we show that the reset anomaly is: (1) very nearly noiseless and (2)can be easily calibrated out. Likewise, we show that large-amplitude RTNaffects only a small and fixed population of pixels. It can therefore betracked using standard pixel operability maps.