The Tracking Tapered Gridded Estimator for the 21-cm power spectrum from the Murchison Widefield Array (MWA) drift scan observations – III. Improved upper limits at z = 8.2 from multiple pointings

Abstract We analyze zenith-pointing (δ = −26. 7○) Murchison Widefield Array (MWA) νc = 154. 2 MHz drift scan observations covering 349. 0○ ≤ α ≤ 70. 0○ with 163 pointing centers (PCs) spaced by 0. 5○. We measure Dℓ, the mean-squared angular brightness temperature fluctuations, as a function of α. A broad peak at α ≈ 50. 0○ corresponds to the bright extended source Fornax A in the main lobe of the primary beam. A smaller peak at α ≈ 5. 0○ possibly corresponds to Fornax A in the first sidelobe. For α ≤ 22. 0○ and ℓ ≥ 200, we find Dℓ∝ℓ2, which we interpret as Poisson fluctuations from point sources. We present Δ2 (k), the mean-squared 21-cm brightness temperature fluctuations from the Epoch of Reionization, as a function of α. Fornax A causes strong contamination near α ≈ 50. 5○, elsewhere several PCs are consistent with noise. The range 358. 5○ ≤ α ≤ 11. 5○ is relatively foreground-free and best suited for EoR science. The PC at α = 11. 0○ yields the best 2σ upper limit ^2 ₔ₋ (k) = (173. 13) ^2\, mK^{2} at k = 0. 161 Mpc−1. We incoherently combine 23 PCs to obtain ₔ₋² (k) = (98. 67) ^2\, mK^2 at k = 0. 156 Mpc−1. This is the tightest upper limit from the MWA, being ≈3 times lower than earlier MWA limits, but ≈2 and ≈21 times higher than the LOFAR and HERA limits, respectively, and ≈3 orders of magnitude above theoretical predictions.