The Tracking Tapered Gridded Estimator for the 21-cm power spectrum from MWA drift scan observations I: Validation and preliminary results
Suman Chatterjee, Khandakar Md Asif Elahi, Somnath Bharadwaj, Shouvik Sarkar, Samir Choudhuri, Shiv Sethi, Akash Kumar Patwa
arXiv:2405.10080v1 Announce Type: new
Abstract: Drift scan observations provide the broad sky coverage and instrumental stability needed to measure the Epoch of Reionization (EoR) 21-cm signal. In such observations, the telescope’s pointing center (PC) moves continuously on the sky. The Tracking Tapered Gridded Estimator (TTGE) combines observations from different PC to estimate $P(k_{perp}, k_{parallel})$ the 21-cm power spectrum, centered on a tracking center (TC) which remains fixed on the sky. The tapering further restricts the sky response to a small angular region around TC, thereby mitigating wide-field foregrounds. Here we consider $154.2 , {rm MHz}$ ($z = 8.2$) Murchison Widefield Array (MWA) drift scan observations. The periodic pattern of flagged channels, present in MWA data, is known to introduce artefacts which pose a challenge for estimating $P(k_{perp}, k_{parallel})$. We demonstrate that the TTGE is able to recover $P(k_{perp}, k_{parallel})$ without any artefacts, and estimate $P(k)$ within $5 %$ accuracy over a large $k$-range. We also present preliminary results for a single PC, combining 9 nights of observation $(17 , {rm min}$ total). We find that $P(k_{perp}, k_{parallel})$ exhibits streaks at a fixed interval of $k_{parallel}=0.29 , {rm Mpc}^{-1}$, which matches $Delta nu_{rm per}=1.28 , {rm MHz}$ that is the period of the flagged channels. The streaks are not as pronounced at larger $k_{parallel}$, and in some cases they do not appear to extend across the entire $k_{perp}$ range. The rectangular region $0.05 leq k_{perp} leq 0.16 , {rm Mpc^{-1}}$ and $0.9 leq k_{parallel} leq 4.6 , {rm Mpc^{-1}}$ is found to be relatively free of foreground contamination and artefacts, and we have used this to place the $2sigma$ upper limit $Delta^2(k) arXiv:2405.10080v1 Announce Type: new
Abstract: Drift scan observations provide the broad sky coverage and instrumental stability needed to measure the Epoch of Reionization (EoR) 21-cm signal. In such observations, the telescope’s pointing center (PC) moves continuously on the sky. The Tracking Tapered Gridded Estimator (TTGE) combines observations from different PC to estimate $P(k_{perp}, k_{parallel})$ the 21-cm power spectrum, centered on a tracking center (TC) which remains fixed on the sky. The tapering further restricts the sky response to a small angular region around TC, thereby mitigating wide-field foregrounds. Here we consider $154.2 , {rm MHz}$ ($z = 8.2$) Murchison Widefield Array (MWA) drift scan observations. The periodic pattern of flagged channels, present in MWA data, is known to introduce artefacts which pose a challenge for estimating $P(k_{perp}, k_{parallel})$. We demonstrate that the TTGE is able to recover $P(k_{perp}, k_{parallel})$ without any artefacts, and estimate $P(k)$ within $5 %$ accuracy over a large $k$-range. We also present preliminary results for a single PC, combining 9 nights of observation $(17 , {rm min}$ total). We find that $P(k_{perp}, k_{parallel})$ exhibits streaks at a fixed interval of $k_{parallel}=0.29 , {rm Mpc}^{-1}$, which matches $Delta nu_{rm per}=1.28 , {rm MHz}$ that is the period of the flagged channels. The streaks are not as pronounced at larger $k_{parallel}$, and in some cases they do not appear to extend across the entire $k_{perp}$ range. The rectangular region $0.05 leq k_{perp} leq 0.16 , {rm Mpc^{-1}}$ and $0.9 leq k_{parallel} leq 4.6 , {rm Mpc^{-1}}$ is found to be relatively free of foreground contamination and artefacts, and we have used this to place the $2sigma$ upper limit $Delta^2(k)