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
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| Format: | Preprint |
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2026
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| _version_ | 1866918481109188608 |
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| author | Sarkar, Shouvik Elahi, Khandakar Md Asif Choudhuri, Samir Bharadwaj, Somnath Chatterjee, Suman Bhattacharyya, Baijayanta Sethi, Shiv Patwa, Akash Kumar |
| author_facet | Sarkar, Shouvik Elahi, Khandakar Md Asif Choudhuri, Samir Bharadwaj, Somnath Chatterjee, Suman Bhattacharyya, Baijayanta Sethi, Shiv Patwa, Akash Kumar |
| contents | We analyze zenith-pointing $(δ=-26.7^{\circ})$ Murchison Widefield Array (MWA) $ν_c=154.2 \,{\rm MHz}$ drift scan observations covering $349.0^{\circ} \le α\le 70.0^{\circ}$ with 163 pointing centers (PCs) spaced by $0.5^{\circ}$. We measure $D_{\ell}$, the mean-squared angular brightness temperature fluctuations, as a function of $α$. A broad peak at $α\approx 50.0^{\circ}$ corresponds to the bright extended source Fornax~A in the main lobe of the primary beam. A smaller peak at $α\approx 5.0^{\circ}$ possibly corresponds to Fornax~A in the first sidelobe. For $α\leq 22.0^{\circ}$ and $\ell \ge 200$, we find $D_{\ell} \propto \ell^2$, which we interpret as Poisson fluctuations from point sources. We present $Δ^2(k)$, the mean-squared 21-cm brightness temperature fluctuations from the Epoch of Reionization, as a function of $α$. Fornax~A causes strong contamination near $α\approx 50.5^{\circ}$, elsewhere several PCs are consistent with noise. The range $358.5^{\circ} \leq α\leq 11.5^{\circ}$ is relatively foreground-free and best suited for EoR science. The PC at $α= 11.0^{\circ}$ yields the best $2σ$ upper limit $Δ^{2}_{\rm UL}(k) = (173.13)^{2}\,{\rm mK^{2}}$ at $k = 0.161\,{\rm Mpc^{-1}}$. We incoherently combine $23$ PCs to obtain $Δ_{\rm UL}^2(k)=(98.67)^{2}\,{\rm mK}^{2}$ at $k=0.156\,{\rm Mpc}^{-1}$. This is the tightest upper limit from the MWA, being $\approx3$ times lower than earlier MWA limits at $z = 8.2$, but $\approx2$ and $\approx21$ times higher than the LOFAR and HERA limits, respectively, and $\approx3$ orders of magnitude above theoretical predictions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_24144 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | 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 Sarkar, Shouvik Elahi, Khandakar Md Asif Choudhuri, Samir Bharadwaj, Somnath Chatterjee, Suman Bhattacharyya, Baijayanta Sethi, Shiv Patwa, Akash Kumar Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics We analyze zenith-pointing $(δ=-26.7^{\circ})$ Murchison Widefield Array (MWA) $ν_c=154.2 \,{\rm MHz}$ drift scan observations covering $349.0^{\circ} \le α\le 70.0^{\circ}$ with 163 pointing centers (PCs) spaced by $0.5^{\circ}$. We measure $D_{\ell}$, the mean-squared angular brightness temperature fluctuations, as a function of $α$. A broad peak at $α\approx 50.0^{\circ}$ corresponds to the bright extended source Fornax~A in the main lobe of the primary beam. A smaller peak at $α\approx 5.0^{\circ}$ possibly corresponds to Fornax~A in the first sidelobe. For $α\leq 22.0^{\circ}$ and $\ell \ge 200$, we find $D_{\ell} \propto \ell^2$, which we interpret as Poisson fluctuations from point sources. We present $Δ^2(k)$, the mean-squared 21-cm brightness temperature fluctuations from the Epoch of Reionization, as a function of $α$. Fornax~A causes strong contamination near $α\approx 50.5^{\circ}$, elsewhere several PCs are consistent with noise. The range $358.5^{\circ} \leq α\leq 11.5^{\circ}$ is relatively foreground-free and best suited for EoR science. The PC at $α= 11.0^{\circ}$ yields the best $2σ$ upper limit $Δ^{2}_{\rm UL}(k) = (173.13)^{2}\,{\rm mK^{2}}$ at $k = 0.161\,{\rm Mpc^{-1}}$. We incoherently combine $23$ PCs to obtain $Δ_{\rm UL}^2(k)=(98.67)^{2}\,{\rm mK}^{2}$ at $k=0.156\,{\rm Mpc}^{-1}$. This is the tightest upper limit from the MWA, being $\approx3$ times lower than earlier MWA limits at $z = 8.2$, but $\approx2$ and $\approx21$ times higher than the LOFAR and HERA limits, respectively, and $\approx3$ orders of magnitude above theoretical predictions. |
| title | 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 |
| topic | Cosmology and Nongalactic Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2604.24144 |