Comparing Redundant and Sky-model-based Interferometric Calibration: A First Look with Phase II of the MWA
Jul 13, 2018Citations per year
Abstract: (arXiv)
Interferometric arrays seeking to measure the 21 cm signal from the Epoch of
Reionization must contend with overwhelmingly bright emission from foreground
sources. Accurate recovery of the 21 cm signal will require precise calibration
of the array, and several new avenues for calibration have been pursued in
recent years, including methods using redundancy in the antenna configuration.
The newly upgraded Phase II of Murchison Widefield Array (MWA) is the first
interferometer that has large numbers of redundant baselines while retaining
good instantaneous UV-coverage. This array therefore provides a unique
opportunity to compare redundant calibration with sky-model based algorithms.
In this paper, we present the first results from comparing both calibration
approaches with MWA Phase II observations. For redundant calibration, we use
the package OMNICAL, and produce sky-based calibration solutions with the
analysis package Fast Holographic Deconvolution (FHD). There are three
principal results. (1) We report the success of OMNICAL on observations of
ORBComm satellites, showing substantial agreement between redundant visibility
measurements after calibration. (2) We directly compare OMNICAL calibration
solutions with those from FHD, and demonstrate these two different calibration
schemes give extremely similar results. (3) We explore improved calibration by
combining OMNICAL and FHD. We evaluate these combined methods using power
spectrum techniques developed for EoR analysis and find evidence for marginal
improvements mitigating artifacts in the power spectrum. These results are
likely limited by signal-to-noise in the six hours of data used, but suggest
future directions for combining these two calibration schemes.Note:
- 20 pages, 11 figures. Accepted to ApJ
- dark ages, reionization, first stars
- instrumentation: interferometers
- methods: data analysis
- techniques: interferometric
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