ABSTRACT The 21 cm transition from neutral hydrogen promises to be the best observational probe of the epoch of reionization (EoR). The main difficulty in measuring the 21 cm signal is the presence of bright foregrounds that require very accurate interferometric calibration. Closure quantities may circumvent the calibration requirements but may be, however, affected by direction-dependent effects, particularly antenna primary beam responses. This work investigates the impact of antenna primary beams affected by mutual coupling on the closure phase and its power spectrum. Our simulations show that primary beams affected by mutual coupling lead to a leakage of foreground power into the EoR window, which can be up to ∼104 times higher than the case where no mutual coupling is considered. This leakage is, however, essentially confined at k < 0.3 h Mpc−1 for triads that include 29 m baselines. The leakage magnitude is more pronounced when bright foregrounds appear in the antenna sidelobes, as expected. Finally, we find that triads that include mutual coupling beams different from each other have power spectra similar to triads that include the same type of mutual coupling beam, indicating that beam-to-beam variation within triads (or visibility pairs) is not the major source of foreground leakage in the EoR window.
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Array element coupling in radio interferometry I: a semi-analytic approach
We derive a general formalism for interferometric visibilities, which considers first-order antenna–antenna coupling and assumes steady-state, incident radiation. We simulate such coupling features for non-polarized skies on a compact, redundantly spaced array and present a phenomenological analysis of the coupling features. Contrary to previous studies, we find mutual coupling features manifest themselves at non-zero fringe rates. We compare power-spectrum results for both coupled and non-coupled (noiseless, simulated) data and find coupling effects to be highly dependent on local sidereal time (LST), baseline length, and baseline orientation. For all LSTs, lengths, and orientations, coupling features appear at delays which are outside the foreground ‘wedge’, which has been studied extensively and contains non-coupled astrophysical foreground features. Further, we find that first-order coupling effects threaten our ability to average data from baselines with identical length and orientation. Two filtering strategies are proposed which may mitigate such coupling systematics. The semi-analytic coupling model herein presented may be used to study mutual coupling systematics as a function of LST, baseline length, and baseline orientation. Such a model is not only helpful to the field of 21cm cosmology, but any study involving interferometric measurements, where coupling effects at the level of at least 1 part in 104 could corrupt the scientific result. Our model may be used to mitigate coupling systematics in existing radio interferometers and to design future arrays where the configuration of array elements inherently mitigates coupling effects at desired LSTs and angular resolutions.
more » « less- NSF-PAR ID:
- 10394566
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 514
- Issue:
- 2
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 1804-1827
- Size(s):
- ["p. 1804-1827"]
- Sponsoring Org:
- National Science Foundation
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