The FHD polarised imaging pipeline: A new approach to widefield interferometric polarimetry

We describe a new polarised imaging pipeline implemented in the FHD software package. The pipeline is based on the optimal mapmaking imaging approach and performs horizon-to-horizon image reconstruction in all polarisation modes. We discuss the formalism behind the pipeline's polarised analysis, describing equivalent representations of the polarised beam response, or Jones matrix. We show that, for arrays where antennas have uniform polarisation alignments, defining a non-orthogonal instrumental polarisation basis enables accurate and efficient image reconstruction. Finally, we present a new calibration approach that leverages widefield effects to perform fully polarised calibration. This analysis pipeline underlies the analysis of Murchison Widefield Array data in Byrne et al. (2022, MNRAS, 510, 2011).