Detectors for the<i>James Webb Space Telescope</i>Near‐Infrared Spectrograph. I. Readout Mode, Noise Model, and Calibration Considerations

Abstract

We describe how the James Webb Space Telescope (JWST) Near-Infrared\nSpectrograph's (NIRSpec's) detectors will be read out, and present a model of\nhow noise scales with the number of multiple non-destructive reads\nsampling-up-the-ramp. We believe that this noise model, which is validated\nusing real and simulated test data, is applicable to most astronomical\nnear-infrared instruments. We describe some non-ideal behaviors that have been\nobserved in engineering grade NIRSpec detectors, and demonstrate that they are\nunlikely to affect NIRSpec sensitivity, operations, or calibration. These\ninclude a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real\ntest data, we show that the reset anomaly is: (1) very nearly noiseless and (2)\ncan be easily calibrated out. Likewise, we show that large-amplitude RTN\naffects only a small and fixed population of pixels. It can therefore be\ntracked using standard pixel operability maps.\n