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Primary Beam Shape Calibration from Mosaicked Observations. Chat Hull Collaborators : Geoff Bower, Peter Williams, Casey Law, Steve Croft, Dave Whysong , Gerry Harp, and the rest of the ATA team GSPS 4 December 2009. The Allen Telescope Array.

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primary beam shape calibration from mosaicked observations
Primary Beam Shape Calibration from Mosaicked Observations

Chat Hull

Collaborators: Geoff Bower, Peter Williams, Casey Law, Steve Croft, Dave Whysong, Gerry Harp, and the rest of the ATA team

GSPS

4 December 2009

the allen telescope array
The Allen Telescope Array
  • Centimeter-wave LNSD interferometer in Hat Creek, CA
  • Commensal observing with SETI
  • Wide-band frequency coverage: 0.5 – 11.2 GHz (3-60 cm)
  • Excellent survey speed (5 deg2 FOV)
  • Present: ATA-42, 6.1-meter antennas
  • Future: ATA-350 – greater sensitivity
beam characterization
Beam characterization
  • Beam: sensitivity relative to the telescope’s pointing center
  • Beam pattern is a sinc function (Airy disk – response of a parabolic antenna)
  • Central portion of the beam is roughly Gaussian
  • Good approximation out to the ~10% level
  • By that point, other effects dominate (sidelobes, reflections)
motivation
Motivation
  • Want to make mosaics
  • Need to have excellent characterization of the primary beam shape
    • My aim: characterize it!
    • Using archival data from ATATS
  • Start with FWHM
  • Canonical value:
same source multiple appearances
Same source, multiple appearances

Pointing 1

Pointing 2

Images courtesy of Steve Croft

  • Can use multiple matches of many sources to characterize the beam
two point gaussian solution1
Two-point Gaussian solution
  • Analytic solution to the Gaussian between two source appearances:
  • r1 , r2  distances from respective pointing centers
  • S1 , S2 fluxes in respective pointings
two point gaussian solution2
Two-point Gaussian solution
  • Solution:
  • Problems: when S1 ≈ S2 and when r1 ≈ r2
problematic pairs
Problematic pairs

Observed flux ratios

problematic pairs1
Problematic pairs

Distance ratios

slide11

BART ticket across the Bay

$3.65

2012 projection of UC Berkeley undergraduate fees

$465,700.31

Not being able to use the best part of your data

Priceless

observed flux pairs
Observed flux pairs

Untrimmed, uncorrected

observed flux pairs1
Observed flux pairs

Trimmed, uncorrected

corrected flux pairs
Corrected flux pairs

Untrimmed, corrected

corrected flux pairs1
Corrected flux pairs

Trimmed, corrected

other beam characterizations
Other beam characterizations
  • Hex-7 results
    • FWHM values close to canonical value
  • Beam holography
    • Slightly larger value
future work
Future work
  • PiGSS data
  • Constrain beam angle and ellipticity
    • Will have to contend with transformation from RA/Dec to Az/El
  • Compare these synthesized results with Gerry’s antenna-by-antenna results
  • Tweak the Gaussian approximation when solving for FWHM
  • Give a more rigorous statistical treatment to the data (MLE?)
conclusions
Conclusions
  • Beam has the expected FWHM!
    • Our value:
    • Telescope is producing the data we expect
  • Arrived at an answer with zero telescope time
  • Potential application to other radio telescopes needing simple beam characterization