TY - JOUR
T1 - First demonstration of ECHO
T2 - An external calibrator for hydrogen observatories
AU - Jacobs, Daniel
AU - Burba, Jacob
AU - Bowman, Judd
AU - Neben, Abraham R.
AU - Stinnett, Benjamin
AU - Turner, Lauren
AU - Johnson, Kali
AU - Busch, Michael
AU - Allison, Jay
AU - Leatham, Marc
AU - Rodriguez, Victoria Serrano
AU - Denney, Mason
AU - Nelson, David
N1 - Funding Information:
ECHO development is supported by a grant from the National Science Foundation AST program through award 1407646. D.C.J. acknowledges support by the NSF Astronomy and Astrophysics Fellowship Program through award 1401708. We thank Rich Bradley and staff at the National Radio Astronomy Observatory, Green Bank and Andri Gretarsson and Embry Riddle Aeronautical Observatory for generously supporting this project with their time and equipment. This project makes use of the Astropy python library (Astropy Collaboration et al. 2013).
Publisher Copyright:
© 2017, The Astronomical Society of the Pacific. All rights reserved.
PY - 2017/3/1
Y1 - 2017/3/1
N2 - Multiple instruments are pursuing constraints on dark energy, observing reionization and opening a window on the dark ages through the detection and characterization of the 21 cm hydrogen line for redshifts ranging from ~1 to 25. These instruments, including CHIME in the sub-meter and HERA in the meter bands, are wide-field arrays with multiple-degree beams, typically operating in transit mode. Accurate knowledge of their primary beams is critical for separation of bright foregrounds from the desired cosmological signals, but difficult to achieve through astronomical observations alone. Previous beam calibration work at low frequencies has focused on model verification and does not address the need of 21 cm experiments for routine beam mapping, to the horizon, of the as-built array. We describe the design and methodology of a drone-mounted calibrator, the External Calibrator for Hydrogen Observatories (ECHO), that aims to address this need. We report on a first set of trials to calibrate lowfrequency dipoles at 137 MHz and compare ECHO measurements to an established beam-mapping system based on transmissions from the Orbcomm satellite constellation. We create beam maps of two dipoles at a 9° resolution and find sample noise ranging from 1% at the zenith to 100% in the far sidelobes. Assuming this sample noise represents the error in the measurement, the higher end of this range is not yet consistent with the desired requirement but is an improvement on Orbcomm. The overall performance of ECHO suggests that the desired precision and angular coverage is achievable in practice with modest improvements. We identify the main sources of systematic error and uncertainty in our measurements and describe the steps needed to overcome them.
AB - Multiple instruments are pursuing constraints on dark energy, observing reionization and opening a window on the dark ages through the detection and characterization of the 21 cm hydrogen line for redshifts ranging from ~1 to 25. These instruments, including CHIME in the sub-meter and HERA in the meter bands, are wide-field arrays with multiple-degree beams, typically operating in transit mode. Accurate knowledge of their primary beams is critical for separation of bright foregrounds from the desired cosmological signals, but difficult to achieve through astronomical observations alone. Previous beam calibration work at low frequencies has focused on model verification and does not address the need of 21 cm experiments for routine beam mapping, to the horizon, of the as-built array. We describe the design and methodology of a drone-mounted calibrator, the External Calibrator for Hydrogen Observatories (ECHO), that aims to address this need. We report on a first set of trials to calibrate lowfrequency dipoles at 137 MHz and compare ECHO measurements to an established beam-mapping system based on transmissions from the Orbcomm satellite constellation. We create beam maps of two dipoles at a 9° resolution and find sample noise ranging from 1% at the zenith to 100% in the far sidelobes. Assuming this sample noise represents the error in the measurement, the higher end of this range is not yet consistent with the desired requirement but is an improvement on Orbcomm. The overall performance of ECHO suggests that the desired precision and angular coverage is achievable in practice with modest improvements. We identify the main sources of systematic error and uncertainty in our measurements and describe the steps needed to overcome them.
KW - Dark ages, reionization, first stars
KW - Instrumentation: interferometers
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U2 - 10.1088/1538-3873/aa56b9
DO - 10.1088/1538-3873/aa56b9
M3 - Article
AN - SCOPUS:85014262920
SN - 0004-6280
VL - 129
JO - Publications of the Astronomical Society of the Pacific
JF - Publications of the Astronomical Society of the Pacific
IS - 973
M1 - 035002
ER -