A demonstration of the effect of fringe-rate filtering in the Hydrogen Epoch of Reionization Array delay power spectrum pipeline

TL;DR

This paper demonstrates how fringe-rate filtering in the Hydrogen Epoch of Reionization Array pipeline can suppress systematic effects and noise, impacting the interpretation of delay power spectra in 21cm cosmology.

Contribution

It introduces specific fringe-rate filters using prolate spheroidal sequences for sidelobe suppression and systematic removal, with analysis on simulated data.

Findings

FR filtering can effectively suppress sidelobe and ground systematics.

Filtering introduces correlations in noise, affecting data interpretation.

Simulations show the impact of filters on power spectrum accuracy.

Abstract

Radio interferometers targeting the 21cm brightness temperature fluctuations at high redshift are subject to systematic effects that operate over a range of different timescales. These can be isolated by designing appropriate Fourier filters that operate in fringe-rate (FR) space, the Fourier pair of local sidereal time (LST). Applications of FR filtering include separating effects that are correlated with the rotating sky vs. those relative to the ground, down-weighting emission in the primary beam sidelobes, and suppressing noise. FR filtering causes the noise contributions to the visibility data to become correlated in time however, making interpretation of subsequent averaging and error estimation steps more subtle. In this paper, we describe fringe rate filters that are implemented using discrete prolate spheroidal sequences, and designed for two different purposes -- beam sidelobe/horizon suppression (the `mainlobe' filter), and ground-locked systematics removal (the `notch' filter). We apply these to simulated data, and study how their properties affect visibilities and power spectra generated from the simulations. Included is an introduction to fringe-rate filtering and a demonstration of fringe-rate filters applied to simple situations to aid understanding.