Direction-Dependent Polarised Primary Beams in Wide-Field Synthesis Imaging

TL;DR

This paper investigates how direction-dependent, polarised primary beams affect wide-field synthesis imaging, proposing methods to improve correction techniques for upcoming Epoch of Reionisation experiments targeting faint 21cm signals.

Contribution

It introduces new approaches for incorporating direction-dependent corrections into visibility gridding kernels, enhancing imaging accuracy for fixed dipole arrays like SKA and HERA.

Findings

Snapshot integration produces more compact gridding kernels.

Alternative kernels can suppress direction-dependent variations by tens of decibels.

Methods reduce the complexity of polarised leakage corrections.

Abstract

The process of wide-field synthesis imaging is explored, with the aim of understanding the implications of variable, polarised primary beams for forthcoming Epoch of Reionisation experiments. These experiments seek to detect weak signatures from redshifted 21cm emission in deep residual datasets, after suppression and subtraction of foreground emission. Many subtraction algorithms benefit from low side-lobes and polarisation leakage at the outset, and both of these are intimately linked to how the polarised primary beams are handled. Building on previous contributions from a number of authors, in which direction-dependent corrections are incorporated into visibility gridding kernels, we consider the special characteristics of arrays of fixed dipole antennas operating around 100-200 MHz, looking towards instruments such as the Square Kilometre Array (SKA) and the Hydrogen Epoch of Reionization Arrays (HERA). We show that integrating snapshots in the image domain can help to produce compact gridding kernels, and also reduce the need to make complicated polarised leakage corrections during gridding. We also investigate an alternative form for the gridding kernel that can suppress variations in the direction-dependent weighting of gridded visibilities by 10s of dB, while maintaining compact support.