# Gridded and direct Epoch of Reionisation bispectrum estimates using the Murchison Widefield Array

## TL;DR

This paper presents two methods for estimating the 21cm bispectrum during the Epoch of Reionisation using MWA data, analyzing foreground contamination and the potential for detection within feasible observation times.

## Contribution

It introduces direct and gridded bispectrum estimators applied to MWA data, compares their performance, and discusses strategies to mitigate foreground bias for future EoR studies.

## Key findings

- Some triangle configurations reach noise-level estimates after 10 hours.
- Equilateral configurations are heavily foreground-contaminated.
- Bispectrum detection may require less observation time than power spectrum detection.

## Abstract

We apply two methods to estimate the 21~cm bispectrum from data taken within the Epoch of Reionisation (EoR) project of the Murchison Widefield Array (MWA). Using data acquired with the Phase II compact array allows a direct bispectrum estimate to be undertaken on the multiple redundantly-spaced triangles of antenna tiles, as well as an estimate based on data gridded to the $uv$-plane. The direct and gridded bispectrum estimators are applied to 21 hours of high-band (167--197~MHz; $z$=6.2--7.5) data from the 2016 and 2017 observing seasons. Analytic predictions for the bispectrum bias and variance for point source foregrounds are derived. We compare the output of these approaches, the foreground contribution to the signal, and future prospects for measuring the bispectra with redundant and non-redundant arrays. We find that some triangle configurations yield bispectrum estimates that are consistent with the expected noise level after 10 hours, while equilateral configurations are strongly foreground-dominated. Careful choice of triangle configurations may be made to reduce foreground bias that hinders power spectrum estimators, and the 21~cm bispectrum may be accessible in less time than the 21~cm power spectrum for some wave modes, with detections in hundreds of hours.