Improved Limits on the 21 cm Signal at <i>z</i> = 6.5–7.0 with the Murchison Widefield Array Using Gaussian Information

Abstract We explore the properties of interferometric data from high-redshift 21 cm measurements using the Murchison Widefield Array (MWA). These data contain the redshifted 21 cm signal, contamination from continuum foreground sources, and radiometric noise. The 21 cm signal from the Epoch of Reionization (EoR) is expected to be highly Gaussian, which motivates the use of the power spectrum as an effective statistical tool for extracting astrophysical information. We find that foreground contamination introduces non-Gaussianity into the distribution of measurements and then use this information to separate Gaussian from the non-Gaussian signal. We present improved upper limits on the 21 cm EoR power spectrum from the MWA using a Gaussian component of the data, based on the existing analysis from C. D. Nunhokee et al. 2025. This is extracted as the best-fitting Gaussian to the measured data. Our best 2 σ (thermal+sample variance) limit for 268 hr of data improves from (30.2 mK) 2 to (23.0 mK) 2 at z = 6.5 for the East–West polarization, and from (39.2 mK) 2 to (21.7 mK) 2 = 470 mK 2 in North–South. The best limits at z = 6.8 ( z = 7.0) improve to P &lt; (25.9 mK) 2 ( P &lt; (32.0 mK) 2 ) and k = 0.18 h Mpc −1 ( k = 0.21 h Mpc −1 ). Results are compared with realistic simulations, which indicate that leakage from foreground contamination is a source of the non-Gaussian behavior.