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Advanced Techniques for Low-Frequency Foreground Mitigation in Radio Astronomy

This paper explores the challenges and solutions for mitigating low-frequency foreground signals in radio astronomy. It focuses on the HI 21cm signal detection between 0.5 to 5.0 GHz, highlighting the complexities of source confusion and calibration errors. We utilize advanced techniques such as real-time source removal, FPGA-based correlation, and innovative calibration methodologies like ionospheric peeling. The project aims for enhanced accuracy in detecting reionization signals, employing a wide-field approach with a focus on staged engineering methodologies for robust data processing.

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Advanced Techniques for Low-Frequency Foreground Mitigation in Radio Astronomy

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  1. Challenge: Low frequency foreground – hot, confused sky 0.5 to 5.0 GHz • HI 21cm signal ~ 10 mK • Foreground: T ~ 100 (/200 MHz)^-2.6 K • Highly ‘confused’: 1 source/deg^2 with S140 > 1 Jy • Synch. smooth ~ 100MHz vs. 21cm lines ~ 1 MHz

  2. Chromatic aberration: Frequency differencing with MHz channels doesn’t work well due to frequency dependent far-out sidelobes 142, 174 MHz

  3. Simulation: effects of residual calibration errors 6C source counts > 1Jy (Smax = 200 Jy)

  4. UVSUB ~ ‘real-time’ source removal IMLIN ~ post-processing freq fitting (3rd order)

  5. Datta+ 09 0.1% 1% For errors constant over 1 day: DNR requirement ~ 0.2% calibration errors

  6. Datta + Bowman in prep 300 hours 0.1% calibration errors UVSUB IMLIN

  7. J. Aguirre, D. Jacobs (Penn), C. Carilli (NRAO) • Focus: Reionization (power spec,CSS,abs) • Very wide field: single dipole + screen • Correlator: FPGA-based from Berkeley wireless lab • Staged engineering: maintain GB test installation  PWA  PSA

  8. PAPER: Staged Engineering • Broad band sleeve dipole + flaps • FPGA-based ‘pocket correlator’ from Berkeley wireless lab • S/W Imaging, calibration, PS analysis: AIPY + Miriad/AIPS => Python + CASA, including ionospheric ‘peeling’ calibration 100MHz 200MHz Beam response BEE2: 5 FPGAs, 500 Gops/s

  9. Western Australian deployment in 2008

  10. PAPER/WA -- 4 Ant, July 2007 RMS ~ 1Jy; DNR ~ 1e4 CygA 1e4Jy Parsons et al. 2009 120MHz 180MHz

  11. Paper – South Africa • Karoo site • 16 elements by Nov 1, 2009 • 32 elements possible by Jan 1

  12. PGB 16 dipole, 3x24hr • scale -10 to 10 Jy • rms ~ 100 mJy • FWHM ~ 20’

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