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arXiv · 2610.03882

The Nancy Grace Roman Space Telescope Wide Field Instrument: Characterization of the Brighter-Fatter Effect in a Roman H4RG-10 Detector using the Talbot Effect

Jennie Paine·Ami Choi·Christopher Merchant·Timothy D. Brandt·Jeffrey Kruk·Joshua E. Schlieder·Edward J. Wollack·Analia Cillis·Jahmour J. Givans·Robert Hill·Christopher Hirata·Dana R. Louie·Gregory Mosby·Anna Porredon·Bernard J. Rauscher·Maxime J. Rizzo·Rujula Yete
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Abstract

The Nancy Grace Roman Space Telescope will conduct several community-driven surveys using its Wide Field Instrument (WFI), which contains 18 Teledyne H4RG-10 near-infrared detectors in the focal plane. Roman's wide area survey to measure weak gravitational lensing places particularly stringent requirements on point spread function (PSF) precision for the WFI. The brighter-fatter effect (BFE) is a nonlinear detector effect caused by the deflection of new charge away from pixels with previously accumulated charge during an exposure. As a result, the PSF measured at the detector depends on the charge contrast between pixels, and therefore the effective PSF for astronomical sources is a function of flux contrast and integration time. We present characterization of the BFE observed in a non-flight H4RG by projecting a grid of bright point sources onto the detector using the Talbot Illuminator at the NASA Goddard Space Flight Center Detector Characterization Lab. We find that the effective area of a pixel decreases by $(-2.18\pm0.04) \times 10^{-6}$ per electron of charge contrast with its neighbors, corresponding to a measurable increase in the effective PSF size over the course of an exposure. Despite charge migration, the total signal detected in the vicinity of a bright source is roughly conserved. We also analyze flat field statistics for the same detector to measure the total inter-pixel nonlinearity (IPNL), which is dominated by BFE. We present a method to correct BFE in H4RG images using the flat field IPNL results, adapted from an extant optical correction technique. The correction reduces the observed BFE by about a factor of 25 as measured by the effective pixel area change, but there is remaining nonlinearity in the corrected data. We discuss possible sources of residual nonlinearity and suggest avenues to investigate optimal BFE correction in Roman survey images.

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Jennie Paine, Ami Choi, Christopher Merchant, Timothy D. Brandt, Jeffrey Kruk, Joshua E. Schlieder, Edward J. Wollack, Analia Cillis, Jahmour J. Givans, Robert Hill, Christopher Hirata, Dana R. Louie, Gregory Mosby, Anna Porredon, Bernard J. Rauscher, Maxime J. Rizzo, Rujula Yete. 2026-10-02. The Nancy Grace Roman Space Telescope Wide Field Instrument: Characterization of the Brighter-Fatter Effect in a Roman H4RG-10 Detector using the Talbot Effect. https://arxiv.org/abs/2610.03882

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