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

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 Δ ²UL(k) = (173.13)²\, mK² at k = 0.161 Mpc−1. We incoherently combine 23 PCs to obtain Δ UL²(k)=(98.67)²\, mK² 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.