Mitigating Internal Instrument Coupling II: A Method Demonstration with the Hydrogen Epoch of Reionization Array

TL;DR

This paper demonstrates a method to remove internal reflection and cross coupling systematics from HERA data, enabling detection of faint 21 cm signals from the Epoch of Reionization with improved accuracy.

Contribution

It applies a previously developed formalism and algorithms to real HERA data, showing effective systematic removal and potential for setting competitive upper limits on the 21 cm power spectrum.

Findings

Systematics hinder detection of targeted EoR modes without removal.

Systematic removal recovers modes down to the noise floor.

HERA's upgraded hardware will further improve systematic control.

Abstract

We present a study of internal reflection and cross coupling systematics in Phase I of the Hydrogen Epoch of Reionization Array (HERA). In a companion paper, we outlined the mathematical formalism for such systematics and presented algorithms for modeling and removing them from the data. In this work, we apply these techniques to data from HERA's first observing season as a method demonstration. The data show evidence for systematics that, without removal, would hinder a detection of the 21 cm power spectrum for the targeted EoR line-of-sight modes in the range 0.2 < k_parallel < 0.5\ h^-1 Mpc. After systematic removal, we find we can recover these modes in the power spectrum down to the integrated noise-floor of a nightly observation, achieving a dynamic range in the EoR window of 10^-6 in power (mK^2 units) with respect to the bright galactic foreground signal. In the absence of other systematics and assuming the systematic suppression demonstrated here continues to lower noise levels, our results suggest that fully-integrated HERA Phase I may have the capacity to set competitive upper limits on the 21 cm power spectrum. For future observing seasons, HERA will have upgraded analog and digital hardware to better control these systematics in the field.