Mitigating calibration errors from mutual coupling with time-domain filtering of 21 cm cosmological radio observations

TL;DR

This paper introduces a time-domain filtering method to mitigate mutual coupling effects in 21 cm cosmological radio observations, significantly reducing foreground contamination and improving calibration accuracy for Epoch of Reionisation studies.

Contribution

The paper presents a novel time-domain filtering approach that reduces calibration errors caused by mutual coupling in radio arrays like HERA, enhancing the detection of the EoR signal.

Findings

Foreground power leakage reduced by 2 orders of magnitude at k=0.5

Filtering leads to more robust calibration solutions

Mitigates non-smooth calibration errors from mutual coupling

Abstract

The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionisation (EoR). This has led to the construction of low-frequency radio interferometric arrays, such as the Hydrogen Epoch of Reionization Array (HERA), aimed at systematically mapping this emission for the first time. Precision calibration, however, is a requirement in 21 cm radio observations. Due to the spatial compactness of HERA, the array is prone to the effects of mutual coupling, which inevitably lead to non-smooth calibration errors that contaminate the data. When unsmooth gains are used in calibration, intrinsically spectrally-smooth foreground emission begins to contaminate the data in a way that can prohibit a clean detection of the cosmological EoR signal. In this paper, we show that the effects of mutual coupling on calibration quality can be reduced by applying custom time-domain filters to the data prior to calibration. We find that more robust calibration solutions are derived when filtering in this way, which reduces the observed foreground power leakage. Specifically, we find a reduction of foreground power leakage by 2 orders of magnitude at k=0.5.