English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Radio interferometer arrays such as HERA consist of many close-packed dishesarranged in a regular pattern, giving rise to a large number of `redundant'baselines with the same length and orientation. Since identical baselinesshould see an identical sky signal, this provides a way of finding a relativegain/bandpass calibration without needing an explicit sky model. In reality,there are many reasons why baselines will not be exactly identical, giving riseto a host of effects that spoil the redundancy of the array and induce spuriousstructure in the calibration solutions if not accounted for. In this paper, weseek to build an understanding of how differences in the primary beam responsebetween antennas affect redundantly-calibrated interferometric visibilities andtheir resulting frequency (delay-space) power spectra. We use simulations tostudy several generic types of primary beam variation, including differences inthe width of the main lobe, the angular and frequency structure of thesidelobes, and the beam ellipticity and orientation. For all of these types, wefind that additional temporal structure is induced in the gain solutions,particularly when bright point sources pass through the beam. In comparison,only a low level of additional spectral structure is induced. The temporalstructure modulates the cosmological 21cm power spectrum, but only at the levelof a few percent in our simulations. We also investigate the possibility ofsignal loss due to decoherence effects when non-redundant visibilities areaveraged together, finding that the decoherence is worst when bright pointsources pass through the beam, and that its magnitude varies significantlybetween baseline groups and types of primary beam variation. Redundantcalibration absorbs some of the decoherence effect however, reducing its impactcompared to if the visibilities were perfectly calibrated.

Patterns of primary beam non-redundancy in close-packed 21 cm array observations