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This study presents a method for characterizing the primary beam shape of the Allen Telescope Array (ATA) using interferometric data. By analyzing the full-width half-maximum (FWHM) of the primary beam, we determine the actual beam shape with high accuracy. Leveraging multiple appearances of the same source in different pointings, we minimize errors and enhance the beam characterization. Results show consistency with established values and techniques, offering a simple yet effective approach for beam analysis in radio telescopes.
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Primary Beam Shape Calibration from Mosaicked, Interferometric Observations Chat Hull Collaborators: Geoff Bower, Steve Croft, Peter Williams, Casey Law, Dave Whysong, and the rest of the ATA team URSI 5 January 2011
Outline Motivation Beam-characterization method Results
The Allen Telescope Array • Centimeter-wave large-number-of-small-dishes (LNSD) interferometer in Hat Creek, CA • Present: ATA-42, 6.1-meter antennas • Wide-band frequency coverage: 0.5 – 11.2 GHz (3-60 cm) • Excellent survey speed (5 deg2 field of view) • Commensal observing with SETI
Motivation • We want to make mosaics • Need to have excellent characterization of the primary beam shape • Primary beam: sensitivity relative to the telescope’s pointing center • Start by characterizing the FWHM of the primary beam using data from ATATS & PiGSS FWHM = 833 pixels Image courtesy of James Gao
PiGSSpointings Bower et al., 2010
Primary-beam characterization • Primary-beam pattern is an Airy disk • Central portion of the beam is well approximated by a Gaussian
Primary-beam characterization • In this work we assume our primary beam is a circular Gaussian. • Our goal: to use ATA data to calculate the actual FWHM of the primary beam at the ATATS and PiGSS frequencies.
Primary-beam characterization • Canonical value of FWHM:
Same source, multiple appearances Pointing 1 Pointing 2 Images courtesy of Steve Croft Can use sources’ multiple appearances to characterize the beam
Same source, multiple appearances Apparent flux densities of the same source in two different pointings • We know the flux densities and the distances from the pointing centers
Least-squaresminimization • Find the FWHM value that minimizes A • Benefits: • Can be extended to fit ellipticity & beam angle
Best-fit FWHM ATATS PiGSS • High A values due to systematic underestimation of flux density errors, non-circularity of the beam, mismatched sources • We see a slightly narrower beam-width, due to imperfect understanding of ATA antenna response, inadequacy of Gaussian beam model
Conclusions • ATA primary beam has the expected FWHM • Our calculated value: • Results are consistent with canonical value (Welch et al.), radio holography (Harp et al.), and the Hex-7 beam characterization technique • Arrived at an answer with zero dedicated telescope time • Potential application to other radio telescopes needing simple beam characterization using science data