Exploring the brighter fatter effect with the Hyper Suprime-Cam

TL;DR

This paper investigates the brighter fatter effect in Hyper Suprime-Cam, demonstrating its origin, modeling it with a scalar kernel, and applying corrections that improve image linearity and PSF consistency.

Contribution

It provides a first-principles derivation of the effect's parametrization and introduces a practical method to estimate and correct it in astronomical images.

Findings

Correction restores linearity in photon transfer curves

Reduces luminosity dependence of the PSF

Kernel-based correction improves image quality

Abstract

The brighter fatter effect has been postulated to arise due to the build up of a transverse electric field, produced as photo-charges accumulate in the pixels' potential wells. We investigate the brighter fatter effect in Hyper Suprime-Cam by examining flat fields and moments of stars. We observe deviations from the expected linear relation in the photon transfer curve, luminosity dependent correlations between pixels in flat field images and a luminosity dependent point spread function (PSF) in stellar observations. Under the key assumptions of translation invariance and Maxwell's equations in the quasi-static limit, we give a first-principles proof that the effect can be parametrized by a translationally invariant scalar kernel. We describe how this kernel can be estimated from flat fields and discuss how this kernel has been used to remove the brighter fatter distortions in Hyper Suprime-Cam images. We find that our correction restores the expected linear relation in the photon transfer curves and significantly reduces, but does not completely remove, the luminosity dependence of the PSF over a wide range of magnitudes.