We compute the spherically-averaged power spectrum from four seasons of data obtained for the Epoch of Reionisation ( EoR ) project observed with the Murchison Widefield Array ( MWA ) .
We measure the EoR power spectrum over k = 0.07 - 3.0 ~ { } h Mpc ^ { -1 } at redshifts z = 6.5 - 8.7 .
The largest aggregation of 110 hours on EoR0 high-band ( 3,340 observations ) , yields a lowest measurement of ( 43 mK ) ^ { 2 } = 1.8 \times 10 ^ { 3 } mK ^ { 2 } at k =0.14 h Mpc ^ { -1 } and z = 6.5 ( 2 \sigma thermal noise plus sample variance ) .
Using the Real-Time System to calibrate and the CHIPS pipeline to estimate power spectra , we select the best observations from the central five pointings within the 2013–2016 observing seasons , observing three independent fields and in two frequency bands .
This yields 13,591 2-minute snapshots ( 453 hours ) , based on a quality assurance metric that measures ionospheric activity .
We perform another cut to remove poorly-calibrated data , based on power in the foreground-dominated and EoR-dominated regions of the two-dimensional power spectrum , reducing the set to 12,569 observations ( 419 hours ) .
These data are processed in groups of 20 observations , to retain the capacity to identify poor data , and used to analyse the evolution and structure of the data over field , frequency , and data quality .
We subsequently choose the cleanest 8,935 observations ( 298 hours of data ) to form integrated power spectra over the different fields , pointings and redshift ranges .