Detection of the weak cosmological signal from high-redshift hydrogen demands careful data analysis and an understanding of the full instrument signal chain. Here, we use the WODEN simulation pipeline to produce realistic data from the Murchison Widefield Array (MWA) Epoch of Reionisation experiment and test the effects of different instrumental systematics through the AusEoRPipe analysis pipeline. The simulations include a realistic full sky model, direction-independent calibration, and both random and systematic instrumental effects. Results are compared to matched real observations. We find that, (i) with a sky-based calibration and power spectrum approach we have need to subtract more than 90% of all unresolved point source flux (10 mJy apparent) to recover 21-cm signal in the absence of instrumental effects; (ii) when including diffuse emission in simulations, some k-modes cannot be accessed, leading to a need for some diffuse emission removal; (iii) the single greatest cause of leakage is an incomplete sky model; and (iv) other sources of errors, such as cable reflections, flagged channels, and gain errors, impart comparable systematic power to one another and less power than the incomplete sky model.

Observations of the 21 cm signal face significant challenges due to bright astrophysical foregrounds that are several orders of magnitude higher than the brightness of the hydrogen line, along with various systematics. Successful 21 cm experiments require accurate calibration and foreground mitigation. Errors introduced during the calibration process such as systematics can disrupt the intrinsic frequency smoothness of the foregrounds, leading to power leakage into the Epoch of Reionisation window. Therefore, it is essential to develop strategies to effectively address these challenges. In this work, we adopt a stringent approach to identify and address suspected systematics, including malfunctioning antennas, frequency channels corrupted by radio frequency interference, and other dominant effects. We implement a statistical framework that utilises various data products from the data processing pipeline to derive specific criteria and filters. These criteria and filters are applied at intermediate stages to mitigate systematic propagation from the early stages of data processing. Our analysis focuses on observations from the Murchison Widefield Array Phase I configuration. Out of the observations processed by the pipeline, our approach selects 18%, totalling 58 h, that exhibit fewer systematic effects. The successful selection of observations with reduced systematic dominance enhances our confidence in achieving 21 cm measurements.

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).

Precise instrumental calibration is of crucial importance to 21-cm cosmology experiments. The Murchison Widefield Array’s (MWA) Phase II compact configuration offers us opportunities for both redundant calibration and sky-based calibration algorithms; using the two in tandem is a potential approach to mitigate calibration errors caused by inaccurate sky models. The MWA Epoch of Reionization (EoR) experiment targets three patches of the sky (dubbed EoR0, EoR1, and EoR2) with deep observations. Previous work in Li et al. (2018) and (2019) studied the effect of tandem calibration on the EoR0 field and found that it yielded no significant improvement in the power spectrum (PS) over sky-based calibration alone. In this work, we apply similar techniques to the EoR1 field and find a distinct result: the improvements in the PS from tandem calibration are significant. To understand this result, we analyse both the calibration solutions themselves and the effects on the PS over three nights of EoR1 observations. We conclude that the presence of the bright radio galaxy Fornax A in EoR1 degrades the performance of sky-based calibration, which in turn enables redundant calibration to have a larger impact. These results suggest that redundant calibration can indeed mitigate some level of model incompleteness error.