1. 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 1

2. 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 deg 2 FOV) Present: ATA-42, 6.1-meter antennas Future: ATA-350 – greater sensitivity 4 December 20092

3. 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) 4 December 20093

4. 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: 4 December 20094

5. Same source, multiple appearances 4 December 20095 Images courtesy of Steve Croft Pointing 1Pointing 2 Can use multiple matches of many sources to characterize the beam

6. Two-point Gaussian solution 4 December 20096

7. Two-point Gaussian solution Analytic solution to the Gaussian between two source appearances: r 1, r 2  distances from respective pointing centers S 1, S 2  fluxes in respective pointings 4 December 20097

8. Two-point Gaussian solution Solution: Problems: when S 1 ≈ S 2 and when r 1 ≈ r 2 4 December 20098

9. Problematic pairs 4 December 20099 Observed flux ratios

10. Problematic pairs 4 December 200910 Distance ratios

11. 4 December 200911 BART ticket across the Bay 2012 projection of UC Berkeley undergraduate fees Not being able to use the best part of your data Priceless $3.65 $465,700.31

12. Observed flux pairs 4 December 200912 Untrimmed, uncorrected

13. Observed flux pairs 4 December 200913 Trimmed, uncorrected

14. Corrected flux pairs 4 December 200914 Untrimmed, corrected

15. Corrected flux pairs 4 December 200915 Trimmed, corrected

16. FWHM values from trimmed data 4 December 200916

17. Finding the best-fit FWHM 4 December 200917

18. Other beam characterizations Hex-7 results – FWHM values close to canonical value Beam holography – Slightly larger value 4 December 200918

19. 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?) 4 December 200919

20. 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 4 December 200920