Performance of a highly sensitive, 19-element, dual-polarization, cryogenic L-band Phased Array Feed on the Green Bank Telescope

• Main Authors: Roshi, D. Anish, Shillue, W, Simon, B, Warnick, K. F, Jeffs, B, Pisano, D. J, Prestage, R, White, S, Fisher, J. R, Morgan, M, Black, R, Burnett, M, Diao, J, Ruzindana, M, van Tonder, V, Hawkins, L, Marganian, P, Chamberlin, T, Ray, J, Pingel, N. M, Rajwade, K, Lorimer, D. R, Rane, A, Castro, J, Groves, W, Jensen, L, Nelson, J. D, Boyd, T, Beasley, A. J
• Format: Journal Article
• Language: English
• Published: 12-03-2018
• Subjects: Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.1803.04473

A new 1.4 GHz 19-element, dual-polarization, cryogenic phased array feed
(PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green
Bank Telescope (GBT) as part of FLAG (Focal L-band Array for the GBT) project.
Commissioning observations of calibrator radio sources show that this receiver
has the lowest reported beamformed system temperature ($T_{\rm sys}$)
normalized by aperture efficiency ($\eta$) of any phased array receiver to
date. The measured $T_{\rm sys}/\eta$ is $25.4 \pm 2.5$ K near 1350 MHz for the
boresight beam, which is comparable to the performance of the current 1.4 GHz
cryogenic single feed receiver on the GBT. The degradation in $T_{\rm
sys}/\eta$ at $\sim$ 4 arcmin (required for Nyquist sampling) and $\sim$ 8
arcmin offsets from the boresight is, respectively, $\sim$ 1\% and $\sim$ 20\%
of the boresight value. The survey speed of the PAF with seven formed beams is
larger by a factor between 2.1 and 7 compared to a single beam system depending
on the observing application. The measured performance, both in frequency and
offset from boresight, qualitatively agree with predictions from a rigorous
electromagnetic model of the PAF. The astronomical utility of the receiver is
demonstrated by observations of the pulsar B0329+54 and an extended HII region,
the Rosette Nebula. The enhanced survey speed with the new PAF receiver will
enable the GBT to carry out exciting new science, such as more efficient
observations of diffuse, extended neutral hydrogen emission from galactic
in-flows and searches for Fast Radio Bursts.