Morales, MiguelStar, Pyxie2024-10-162024-10-162024-10-162024Star_washington_0250E_27301.pdfhttps://hdl.handle.net/1773/52607Thesis (Ph.D.)--University of Washington, 2024This work advances our goal of understanding the Epoch of Reionization (EoR) by measuring the 21-centimeter line from neutral hydrogen. As the very first stars formed during the EoR, they released ultraviolet light which ionized the surrounding hydrogen until the whole universe was reionized about a billion years after the Big Bang. We probe the EoR by measuring the 21-centimeter line from neutral hydrogen. Detecting this faint signal will unlock mysteries of the universe, identifying primary drivers of the evolution into the structures we see today, as well as constraining theories of the very beginning of the universe and informing mechanics of present-day star and galaxy formation.We use measurements from the Murchison Widefield Array (MWA) to detect the signal from the EoR. In order to uncover the faint signal of the 21-centimeter line we must remove the instrument response from our data with a precision of a part in 10^(-5). While our calibration procedures remove the linear instrument response, nonlinear artifacts remain. We show the effects of these artifacts and identify a source: quantization in the digital signal pathway. Like most instruments, the MWA employs requantization throughout the signal path to combat bit growth between digital signal processing components. We use the Van Vleck correction to remove the effects of one of these requantization stages: the 4-bit requantization immediately before correlation. Then, we model the signal path to develop a correction for an incorrectly implemented requantization stage within the correlator polyphase filterbank between the subfilters and the FFT. These two corrections result in promising improvements to our data quality and analyses. Partly motivated by this work, the MWA collaboration decided to eliminate requantization stages in the new MWA correlator. The first upgrade introduced for MWA Phase III, the MWAX correlator, was commissioned in 2021 and officially replaced the Legacy correlator in 2022. We inspect data from the 2021 EoR commissioning data taken with the new MWAX correlator for artifacts from digital nonlinearities and show that there are significant improvements to data quality. We then analyze the 2021 data to obtain the first power spectrum limit for MWA Phase III. This requires revalidating our calibration approach, updating our flagging and averaging settings for the new correlator data, and retuning our radio frequency interference (RFI) detection for the 2021 RFI environment. We perform data selection quality cuts to obtain our final set of 180 observations with a total of ~5.569 hours of data. Our power spectrum limit has promising results, revealing a drop in contamination from residual nonlinearities in the data. We calculate a lowest upper limit of ∆^2 ≤ 1.76x10^4 mK^2 with our relatively small 2021 commissioning data set, and are hopeful that adding Phase III data from later observing seasons to this analysis would lead to state of the art constraints on the Epoch of Reionization.application/pdfen-USCC BYPhysicsPhysicsThesis