Commissioning the H i Observing Mode of the Beam Former for the Cryogenically Cooled Focal L-band Array for the GBT (FLAG)

• Published in: The Astronomical journal Vol. 161; no. 4; p. 163
• Main Authors: Pingel, N. M., Pisano, D. J., Ruzindana, M., Burnett, M., Rajwade, K. M., Black, R., Jeffs, B., Warnick, K. F., Lorimer, D. R., Roshi, D. Anish, Prestage, R., McLaughlin, M. A., Agarwal, D., Chamberlin, T., Hawkins, L., Jensen, L., Marganian, P., Nelson, J. D., Shillue, W., Smith, E., Simon, B., Tonder, V. Van, White, S.
• Format: Journal Article
• Language: English
• Published: Madison IOP Publishing 01.04.2021
• Subjects: Astronomy; Beamforming; Commissioning; COMPUTER CODES; Flags; Focal plane; Frequency ranges; Hydrogen; Image quality; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; L-band receivers; Line spectra; MATHEMATICAL METHODS AND COMPUTING; MHZ RANGE; NOISE; Phased arrays; RADIO TELESCOPES; Receivers & amplifiers; SENSITIVITY; STABILITY; Telescopes
• ISSN: 0004-6256; 1538-3881; 1538-3881
• DOI: 10.3847/1538-3881/abdec2

Abstract We present the results of commissioning observations for a new digital beam-forming back end for the Focal plane L -band Array for the Robert C. Byrd Green Bank Telescope (FLAG), a cryogenically cooled Phased Array Feed (PAF) with the lowest measured T sys / η of any PAF outfitted on a radio telescope to date. We describe the custom software used to apply beam-forming weights to the raw element covariances to create research-quality spectral-line images for the new fine-channel mode, study the stability of the beam weights over time, characterize FLAG’s sensitivity over a frequency range of 150 MHz, and compare the measured noise properties and observed distribution of neutral hydrogen emission from several extragalactic and Galactic sources with data obtained with the current single-pixel L -band receiver. These commissioning runs establish FLAG as the preeminent PAF receiver currently available for spectral-line observations on the world’s major radio telescopes.