The Tracking Tapered Gridded Estimator for the 21-cm power spectrum from MWA drift scan observations II: The Missing Frequency Channels
Khandakar Md Asif Elahi, Somnath Bharadwaj, Suman Chatterjee, Shouvik Sarkar, Samir Choudhuri, Shiv Sethi, Akash Kumar Patwa
arXiv:2410.11380v2 Announce Type: replace
Abstract: Missing frequency channels pose a problem for estimating $P(k_perp,k_parallel)$ the redshifted 21-cm power spectrum (PS) from radio-interferometric visibility data. This is particularly severe for the Murchison Widefield Array (MWA), which has a periodic pattern of missing channels that introduce spikes along $k_parallel$. The Tracking Tapered Gridded Estimator (TTGE) overcomes this by first correlating the visibilities in the frequency domain to estimate the multi-frequency angular power spectrum (MAPS) $C_ell(Deltanu)$ that has no missing frequency separation $Deltanu$. We perform a Fourier transform along $Deltanu$ to estimate $P(k_perp,k_parallel)$. Considering our earlier work, simulations demonstrate that the TTGE can estimate $P(k_perp,k_parallel)$ without any artifacts due to the missing channels. However, the spikes were still found to persist for the actual data, which is foreground-dominated. The current work presents a detailed investigation considering both simulations and actual data. We find that the spikes arise due to a combination of the missing channels and the strong spectral dependence of the foregrounds. Based on this, we propose and demonstrate a technique to mitigate the spikes. Applying this, we find the values of $P(k_perp,k_parallel)$ in the region $0.004 leq k_perp leq 0.048,{rm Mpc^{-1}}$ and $k_parallel > 0.35 ,{rm Mpc^{-1}}$ to be consistent with zero within the expected statistical fluctuations. We obtain the $2sigma$ upper limit of $Delta_{rm UL}^2(k)=(918.17)^2,{rm mK^2}$ at $k=0.404,{rm Mpc^{-1}}$ for the mean squared brightness temperature fluctuations of the $z=8.2$ epoch of reionization (EoR) 21-cm signal. This upper limit is from just $sim 17$ minutes of observation for a single pointing direction. We expect tighter constraints when we combine all $162$ different pointing directions of the drift scan observation.arXiv:2410.11380v2 Announce Type: replace
Abstract: Missing frequency channels pose a problem for estimating $P(k_perp,k_parallel)$ the redshifted 21-cm power spectrum (PS) from radio-interferometric visibility data. This is particularly severe for the Murchison Widefield Array (MWA), which has a periodic pattern of missing channels that introduce spikes along $k_parallel$. The Tracking Tapered Gridded Estimator (TTGE) overcomes this by first correlating the visibilities in the frequency domain to estimate the multi-frequency angular power spectrum (MAPS) $C_ell(Deltanu)$ that has no missing frequency separation $Deltanu$. We perform a Fourier transform along $Deltanu$ to estimate $P(k_perp,k_parallel)$. Considering our earlier work, simulations demonstrate that the TTGE can estimate $P(k_perp,k_parallel)$ without any artifacts due to the missing channels. However, the spikes were still found to persist for the actual data, which is foreground-dominated. The current work presents a detailed investigation considering both simulations and actual data. We find that the spikes arise due to a combination of the missing channels and the strong spectral dependence of the foregrounds. Based on this, we propose and demonstrate a technique to mitigate the spikes. Applying this, we find the values of $P(k_perp,k_parallel)$ in the region $0.004 leq k_perp leq 0.048,{rm Mpc^{-1}}$ and $k_parallel > 0.35 ,{rm Mpc^{-1}}$ to be consistent with zero within the expected statistical fluctuations. We obtain the $2sigma$ upper limit of $Delta_{rm UL}^2(k)=(918.17)^2,{rm mK^2}$ at $k=0.404,{rm Mpc^{-1}}$ for the mean squared brightness temperature fluctuations of the $z=8.2$ epoch of reionization (EoR) 21-cm signal. This upper limit is from just $sim 17$ minutes of observation for a single pointing direction. We expect tighter constraints when we combine all $162$ different pointing directions of the drift scan observation.