UBC Theses and Dissertations
Redundant baseline calibration in CHIME : a first implementation & application as beam probe Good, Deborah C.
The nature of dark energy is one of the most intriguing scientific questions of the twenty-first century. There are many ways to probe dark energy, but one method involves detecting baryon acoustic oscillations (BAO) throughout the universe's history. BAO have a characteristic size scale and therefore act as a ``standard ruler,'' an advantageous property for a method of tracking the universe's expansion history. While baryon acoustic oscillations can be probed in many ways, one of the most intriguing and promising methods is through twenty-one centimeter hydrogen intensity mapping. Several experiments devoted to twenty-one centimeter hydrogen mapping will be coming on line in coming years, and these experiments have stringent calibration requirements due to the need to remove bright foreground signals. These calibration requirements necessitate new and improved methods for calibration. One proposed method is redundant baseline calibration, a self-calibration method which takes advantage of the massively redundant designs of many hydrogen intensity mapping experiments. With the Canadian Hydrogen Intensity Mapping Experiment as a test case, we demonstrate that the redundant baseline method is effective in even its simplest implementation for an idealized version of a real telescope. We then show that redundant baseline calibration fails in real CHIME Pathfinder data in a way that is consistent with deviations from redundancy observed in processed CHIME Pathfinder data. These deviations from redundancy are themselves consistent with the effects of feed-to-feed beam pattern variations, a possibility not considered in the conventional redundant baseline calibration algorithm. We simulate the CHIME Pathfinder including beam width perturbations and verify that similar failures in the redundant baseline calibration can be generated with beam perturbations. We then use the principles of redundant baseline calibration to solve for our simulated beam perturbations. Finally, we compare redundant baseline calibration results to point source holography results and show that the two are equivalent probes of relative feed-to-feed beam variation. We conclude that redundant baseline calibration is a promising path forward in calibrating hydrogen intensity mapping experiments, both as a conventional calibration method and as a probe of beam structure
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