The tracking tapered gridded estimator for the 21-cm power spectrum from MWA drift scan observations-II. the missing frequency channels

Abstract

Missing frequency channels pose a problem in estimating the redshifted 21-cm power spectrum from radio-interferometric visibility data. This is particularly severe for the Murchison Widefield Array (MWA), which has a periodic pattern of missing channels that introduces spikes along. The Tracking Tapered Gridded Estimator (TTGE) overcomes this by first correlating the visibilities in the frequency domain to estimate the multifrequency angular power spectrum (MAPS) that has no missing frequency separation. We perform a Fourier transform along to estimate. Simulations demonstrate that the TTGE can estimate without any artefacts due to missing channels. However, the spikes persist for the actual foreground-dominated data. A detailed investigation, considering both simulations and actual data, reveals that the spikes originate from a combination of the missing channels and the strong spectral dependence of the foregrounds. We propose and demonstrate a technique to mitigate the spikes. Applying this, we find the values of in the region and 0.35 \, {\rm Mpc^{-1}}$]]> to be consistent with zero within the expected statistical fluctuations. We obtain the upper limit of at for the mean-squared brightness temperature fluctuations of the epoch of reionization (EoR) 21-cm signal. This upper limit is from min of observation for a single pointing direction. We expect tighter constraints when we combine all 162 different pointing directions of the drift scan observation.