Redundant-baseline calibration of the hydrogen epoch of reionization array
Joshua S. Dillon, Max E. Lee, Zaki S. Ali, Aaron R. Parsons, Naomi Orosz, Chuneeta D. Nunhokee, Paul La Plante, Adam P. Beardsley, Nicholas S. Kern, Zara Abdurashidova, James Aguirre, Paul Alexander, Yanga Balfour, G. Bernardi, Tashalee S. Billings, Judd D. Bowman, Richard F. Bradley, Philip Bull, Jacob Burba, Steve Carey, C. L. Carilli, Carina Cheng, David R. DeBoer, Matt Dexter, Eloy de Lera Acedo, John Ely, Aaron Ewall‐Wice, Nicolas Fagnoni, Randall Fritz, Steven R. Furlanetto, Kingsley Gale‐Sides, Brian Glendenning, Deepthi Gorthi, Bradley Greig, Jasper Grobbelaar, Ziyaad Halday, B. J. Hazelton, Jacqueline N. Hewitt, J. Hickish, Daniel Jacobs, Austin Julius, Joshua Kerrigan, Piyanat Kittiwisit, Saul A. Kohn, Matthew Kolopanis, Adam Lanman, Telalo Lekalake, David Lewis, Adrian Liu, Yin-Zhe Ma, David H. E. MacMahon, Lourence Malan, Cresshim Malgas, Matthys Maree, Zachary E. Martinot, Eunice Matsetela, Andrei Mesinger, Mathakane Molewa, M. F. Morales, Tshegofalang Mosiane, Steven Murray, Abraham R. Neben, Bojan Nikolic, Robert Pascua, Nipanjana Patra, Samantha Pieterse, Jonathan C. Pober, N. Razavi‐Ghods, Jon Ringuette, James Robnett, Kathryn Rosie, Mário G. Santos, Peter Sims, Craig Smith, Angelo Syce, Max Tegmark, Nithyanandan Thyagarajan, Peter K. G. Williams, Haoxuan Zheng
Abstract
ABSTRACT In 21-cm cosmology, precision calibration is key to the separation of the neutral hydrogen signal from very bright but spectrally smooth astrophysical foregrounds. The Hydrogen Epoch of Reionization Array (HERA), an interferometer specialized for 21-cm cosmology and now under construction in South Africa, was designed to be largely calibrated using the self-consistency of repeated measurements of the same interferometric modes. This technique, known as redundant-baseline calibration resolves most of the internal degrees of freedom in the calibration problem. It assumes, however, on antenna elements with identical primary beams placed precisely on a redundant grid. In this work, we review the detailed implementation of the algorithms enabling redundant-baseline calibration and report results with HERA data. We quantify the effects of real-world non-redundancy and how they compare to the idealized scenario in which redundant measurements differ only in their noise realizations. Finally, we study how non-redundancy can produce spurious temporal structure in our calibration solutions – both in data and in simulations – and present strategies for mitigating that structure.