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We encourage all MWA users to test this new capability for any observations in the first observing semester of 2023. Starting in the second observing semester of 2023, fringe stopping will be the default mode for all MWA observations. Observations without fringe stopping will continue to be supported on an opt-out basis.

Usage

Fringe stopping is available on an opt-in basis for any observation during the first observing semester of 2023. Users may request fringe stopping at the time of scheduling, or at any time prior to the start of the observation. There is no change to how observation data is delivered and no software changes are required to use it, apart from that you should not tell Birli to apply geometric corrections to a fringe-stopping observation. By default, Birli will detect whether an observation was made with fringe-stopping, and geometric corrections will not be run unless explicitly specified at the command line or selected in ASVO.

Implementation

A technical summary of the MWAX fringe stopping implementation will be published soon as part of the forthcoming MWAX paper, a detailed description of the design and validation will be published shortly thereafter.

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Diagram: Comparison of geometric corrections process for using Birli and fringe-stopping

Usage

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and

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fringe-stopping

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Validation

Fringe stopping has been validated against the output of Birli and shown to produce identical results in tests involving hand-crafted data, designed to test particular aspects of its behaviour in isolation. Results on real-world data, from running fringe stopping on live observations simultaneously with Birli in a split-mode configuration, have shown fringe-stopping to perform comparably to Birli on short integration times and fine frequency averaging, and with superior results on longer integration times and coarser channel averaging.

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Diagram: Time-phase plots for fringe stopping (blue) vs Birli (gold) for five baselines (rows) at increasing integration times (columns, 0.5s, 1s, 2s, 4s, 8s).

Diagram: Frequency-phase plots for fringe stopping (left) vs Birli (right), using hand-crafted data to examine phase slopes at an instant in time.