Optimising MWA EoR data processing for improved 21 cm power spectrum measurements -- fine-tuning ionospheric corrections

TL;DR

This paper enhances the calibration process of the MWA for 21 cm EoR observations, significantly reducing foreground contamination and improving prospects for detecting the faint cosmological signal.

Contribution

It introduces refined calibration techniques, including ionospheric correction methods, that improve the power spectrum measurement accuracy for the MWA EoR project.

Findings

At least 2-fold reduction in EoR window power contamination.

Refined calibration configuration improves foreground mitigation.

Method of interpolated ionospheric phase screens enhances correction performance.

Abstract

The redshifted cosmological 21 cm signal emitted by neutral hydrogen during the first billion years of the universe is much fainter relative to other galactic and extragalactic radio emissions, posing a great challenge towards detection of the signal. Therefore, precise instrumental calibration is a vital prerequisite for the success of radio interferometers such as the Murchison Widefield Array (MWA), which aim for a 21 cm detection. Over the previous years, novel calibration techniques targeting the power spectrum paradigm of EoR science have been actively researched and where possible implemented. Using recently acquired computation resources for the MWA, we test the full capabilities of the state-of-the-art calibration techniques available for the MWA EoR project, with a focus on both direction dependent and direction independent calibration. Specifically, we investigate improvements that can be made in the vital calibration stages of sky modelling, ionospheric correction, and compact source foreground subtraction as applied in the hybrid foreground mitigation approach (one that combines both foreground subtraction and avoidance). Additionally, we investigate a method of ionospheric correction using interpolated ionospheric phase screens and assess its performance in the power spectrum space. Overall, we identify a refined RTS calibration configuration that leads to an at least 2 factor reduction of the EoR window power contamination at the $0.1 \; \text{hMpc}^{-1}$ scale. The improvement marks a step further towards detecting the 21 cm signal using the MWA and the forthcoming SKA low telescope.