CaltechAUTHORS
Published August 2025 | Version Published
Journal Article Open

Investigating Mutual Coupling in the Hydrogen Epoch of Reionization Array and Mitigating its Effects on the 21-cm Power Spectrum

Creators

  • 1. ROR icon Massachusetts Institute of Technology
  • 2. ROR icon McGill University
  • 3. ROR icon University of Cambridge
  • 4. ROR icon University of California, Berkeley
  • 5. ROR icon University of Pennsylvania
  • 6. ROR icon South African Radio Astronomy Observatory
  • 7. ROR icon Winona State University
  • 8. ROR icon Arizona State University
  • 9. ROR icon Istituto di Radioastronomia di Bologna
  • 10. ROR icon Rhodes University
  • 11. ROR icon University of Manchester
  • 12. ROR icon University of the Western Cape
  • 13. ROR icon California Institute of Technology
  • 14. ROR icon Indian Institute of Technology Madras
  • 15. ROR icon University of California, Los Angeles
  • 16. ROR icon Institut d'Astrophysique Spatiale
  • 17. ROR icon University of Washington
  • 18. ROR icon Brown University
  • 19. ROR icon Stellenbosch University
  • 20. ROR icon Scuola Normale Superiore di Pisa
  • 21. ROR icon University of Nevada, Las Vegas
  • 22. ROR icon Australian National University
  • 23. ROR icon National Radio Astronomy Observatory
  • 24. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 25. ROR icon American Astronomical Society

Abstract

Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on the 21-cm power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order to detect the 21-cm signal, and simulations that reproduce effects seen in the data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of data from the Hydrogen Epoch of Reionization Array and compare the data against simulations that include a computationally efficient and physically motivated semi-analytic treatment of mutual coupling. We find that simulated coupling features qualitatively agree with coupling features in the data; however, coupling features in the data are brighter than the simulated features, indicating the presence of additional coupling mechanisms not captured by our model. We explore the use of fringe-rate filters as mutual coupling mitigation tools and use our simulations to investigate the effects of mutual coupling on a simulated cosmological 21-cm power spectrum in a 'worst case' scenario where the foregrounds are particularly bright. We find that mutual coupling contaminates a large portion of the 'EoR Window', and the contamination is several orders-of-magnitude larger than our simulated cosmic signal across a wide range of cosmological Fourier modes. While our fiducial fringe-rate filtering strategy reduces mutual coupling by roughly a factor of 100 in power, a non-negligible amount of coupling cannot be excised with fringe-rate filters, so more sophisticated mitigation strategies are required.

Copyright and License

© The Author(s) 2025. Published by Oxford University Press on behalf of Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

Acknowledgement

We thank Vincent MacKay, Bang Nhan, and Jonathan Sievers for discussions which contributed to this work. This material is based upon work supported by the National Science Foundation under Grant Nos. 1636646, 1836019, AST-2144995, and institutional support from the HERA collaboration partners. This research is funded in part by the Gordon and Betty Moore Foundation through Grant GBMF5212to the Massachusetts Institute of Technology. This work was funded in part by the Canada 150 Research Chairs Program. HERA is hosted by the South African Radio Astronomy Observatory, which is a facility of the National Research Foundation, an agency of the Department of Science and Innovation.

AL and RP acknowledge support from the Trottier Space Institute, the Canadian Institute for Advanced Research (CIFAR) Azrieli Global Scholars program, a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant, a NSERC/Fonds de recherche du Québec -Nature et Technologies NOVA grant, the Sloan Research Fellowship, and the William Dawson Scholarship at McGill. EdLA is supported by a Science and Technology Facilities Council (STFC) Ernest Rutherford Fellowship. NK acknowledges support from the National Aeronautics and Space Administration (NASA) through the NASA Hubble Fellowship grant #HST-HF2-51533.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555. This result is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement no. 948764; PB, JB, MJW). SGM has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 101067043. YZM is supported by the National Research Foundation of South Africa with grant numbers 150580, 159044, CHN22111069370, and ERC23040389081.

Data Availability

The data products used in this analysis may be requested via email from the authors. Information on the calibration and LST-binning routines are found in HERA Memo 124 (Dillon et al. 2023). Visibility data were managed using pyuvdata (Hazelton et al. 2017). Inpainting and fringe-rate filtering was performed using tools available in hera_cal (HERA Collaboration 2023b). Power spectrum estimation was performed using tools available in hera_pspec. Visibility simulation was performed with matvis3 (Kittiwisit et al. 2025) using wrappers provided by hera_sim. A demonstration of how to apply the first-order coupling formalism to interferometric visibility data is provided in a tutorial notebook in the hera_sim repository.

Files

staf1012.pdf

Files (2.4 MB)

Name Size Download all
md5:9987bd38dcb2d326162dd89bdeee5e48
2.4 MB Preview Download

Additional details

Related works

Is new version of
Discussion Paper: arXiv:2406.08549 (arXiv)

Funding

National Science Foundation
1636646
National Science Foundation
1836019
National Science Foundation
AST-2144995
Gordon and Betty Moore Foundation
GBMF5212
Canada Research Chairs
Canadian Institute for Advanced Research
Natural Sciences and Engineering Research Council
Fonds de Recherche du Québec – Nature et Technologies
Alfred P. Sloan Foundation
McGill University
Science and Technology Facilities Council
Ernest Rutherford Fellowship -
National Aeronautics and Space Administration
HST-HF2-51533.001-A
Space Telescope Science Institute
National Aeronautics and Space Administration
NAS5-26555
European Research Council
948764
European Union
101067043
National Research Foundation
150580
National Research Foundation
159044
National Research Foundation
CHN22111069370
National Research Foundation
ERC23040389081

Dates

Accepted
2025-05-16
Available
2025-06-27
Published
Available
2025-07-11
Corrected and typeset

Caltech Custom Metadata

Caltech groups
Division of Physics, Mathematics and Astronomy (PMA)
Publication Status
Published