Imaging and Modeling Data from the Hydrogen Epoch of Reionization Array

We discuss absolute calibration strategies for Phase I of the Hydrogen Epoch of Reionization Array (HERA),which aims to measure the cosmological 21 cm signal from the Epoch of Reionization. HERA is a drift-scan arraywith a 10° wide field of view, meaning bright, well-characterized point-source transits are scarce. This, combinedwith HERA’s redundant sampling of the uv plane and the modest angular resolution of the Phase I instrument,make traditional sky-based and self-calibration techniques difficult to implement with high dynamic range.Nonetheless, in this work, we demonstrate calibration for HERA using point-source catalogs and electromagneticsimulations of its primary beam. We show that unmodeled diffuse flux and instrumental contaminants can corruptthe gain solutions and present a gain-smoothing approach for mitigating their impact on the 21 cm power spectrum.We also demonstrate a hybrid sky and redundant calibration scheme and compare it to pure sky-based calibration,showing only a marginal improvement to the gain solutions at intermediate delay scales. Our work suggests thatthe HERA Phase I system can be well calibrated for a foreground avoidance power spectrum estimator by applyingdirection-independent gains with a small set of degrees of freedom across the frequency and time axes.