Characterization of CHIME0s Complex Gain Using New Transits of CygA and CasA Hertig, Emilie Marie
This work aims to improve the calibration of the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a new radiotelescope built in Penticton (BC) and inaugurated in 2017. CHIME’s main goal is to observe baryon acoustic oscillations in order to probe the evolution of the universe at redshifts between 0.8 and 2.5, in the period where the standard model of cosmology predicts that dark energy started to dominate over matter and radiation. Accurate expansion measurements during this period would provide tighter constraints on the Hubble parameter and the dark energy equation of state. This would lead to invalidation or further verification of our current cosmological theories, therefore improving our understanding of the nature of dark energy. It has been observed that the the steel structures of the telescope, as well as the cables and antennae have temperature-dependent behaviour, which affects the quality of the data. Previous attempts of characterizing this dependency weren’t successful; therefore, this works aims to explore an innovative method based on new direct sky observations and allowing to determine the influence of external temperature on CHIME’s complex gain. Thermal susceptibilities are obtained from analyzing observations of bright radiosources, mainly CygA and CasA, and calculating linear fits of the gain fractional variation as a function of external temperature. A correction for the nonlinear behaviour of antennae, based on laboratory experiments, is included in later stages of the analysis, as well as a detailed investigation and treatment of outliers. This project is a step towards the making of a full thermal model that could be included in CHIME’s calibration algorithm in order to significantly improve the quality of cosmological data.
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