The impact of the brighter-fatter effect on the performance of the JWST fine guidance sensor

Neil Rowlands; Calvin Midwinter; Gerry Warner

doi:10.1117/12.2312338

1 August 2018 The impact of the brighter-fatter effect on the performance of the JWST fine guidance sensor

Neil Rowlands, Calvin Midwinter, Gerry Warner

Proceedings Volume 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII; 107091K (2018) https://doi.org/10.1117/12.2312338
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

Abstract

The James Webb Space Telescope Fine Guidance Sensor has two Guider channels. Each channel makes use of 2048x2048 pixel, five micron cutoff H2RG HgCdTe detectors from Teledyne Imaging Systems. Due to their simple unit cell architecture, these detectors exhibit a variety of non-ideal behaviours which can impact the guiding function. In this paper, we examine the potential impact of one of these behaviours, the brighter-fatter effect, using a simulation based on a parameter derived from test results. The brighter-fatter effect (BFE) is the deflection of incoming photo-electrons to adjacent pixels due to the accumulated charge in the central pixel. The simulation model we use is based on the assumption that the effective area of a given pixel is reduced by some factor times the current signal contrast (difference) between adjacent pixels. Combining this with a PSF model for the FGS we can assess systematic differences between the image centroids with and without the BFE effect. A BFE strength parameter was defined and model runs were performed with a range of BFE strengths. In physical terms this parameter is the fractional reduction in effective pixel area per accumulated signal electron. Comparison of the modeled PSF FWHM as a function of this strength parameter with FGS test data provided a measure of the BFE strength parameter for the Guider detectors. With this BFE strength parameter we then ran centroiding simulations and found that there were no significant systematic offsets with respect to star brightness for this level of BFE. The magnitude of the BFE effect would have to be more than 10x greater than that observed before significant centroid offsets on the order of a milli-arcsecond would occur.

Conference Presentation

Citation Download Citation

Neil Rowlands, Calvin Midwinter, and Gerry Warner "The impact of the brighter-fatter effect on the performance of the JWST fine guidance sensor", Proc. SPIE 10709, High Energy, Optical, and Infrared Detectors for Astronomy VIII, 107091K (1 August 2018); https://doi.org/10.1117/12.2312338

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