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Title: The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages

Abstract

Detection of the global H i 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground-/space-based experiments. The crucial spectral features in the global 21 cm signal (turning points) occur at low radio frequencies ≲100 MHz. In addition to the human-generated radio frequency interference, Earth’s ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption, and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21 cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21 cm experiments. The fluctuations in the ionosphere are influenced by solar activity with flicker noise characteristics. The same characteristics are reflected in the ionospheric corruption to any radio signal passing through the ionosphere. As a result, any ground-based observations of the faint global 21 cm signal are corrupted by flicker noise (or 1/f noise, where f is the dynamical frequency) which scales as ν{sup −2} (where ν is the frequency of radio observation) in the presence of a bright galactic foregroundmore » (∝ν{sup −s}, where s is the radio spectral index). Hence, the calibration of the ionosphere for any such experiment is critical. Any attempt to calibrate the ionospheric effects will be subject to the inaccuracies in the current ionospheric measurements using Global Positioning System (GPS) ionospheric measurements, riometer measurements, ionospheric soundings, etc. Even considering an optimistic improvement in the accuracy of GPS–total electron content measurements, we conclude that Earth’s ionosphere poses a significant challenge in the absolute detection of the global 21 cm signal below 100 MHz.« less

Authors:
;  [1];  [2];  [3]; ;  [4]
  1. Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Science, University of Colorado, Boulder, C0 80309 (United States)
  2. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
  3. Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom)
  4. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
Publication Date:
OSTI Identifier:
22868558
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 831; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; CALIBRATION; DISTURBANCES; EMISSION; INTERFERENCE; IONOSPHERE; NOISE; RADIOWAVE RADIATION; REFRACTION; RIOMETERS; SOLAR ACTIVITY; SOUND WAVES; SPACE; STARS; STELLAR ATMOSPHERES

Citation Formats

Datta, Abhirup, Burns, Jack O., Bradley, Richard, Harker, Geraint, Komjathy, Attila, and Lazio, T. Joseph W.,. The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages. United States: N. p., 2016. Web. doi:10.3847/0004-637X/831/1/6.
Datta, Abhirup, Burns, Jack O., Bradley, Richard, Harker, Geraint, Komjathy, Attila, & Lazio, T. Joseph W.,. The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages. United States. https://doi.org/10.3847/0004-637X/831/1/6
Datta, Abhirup, Burns, Jack O., Bradley, Richard, Harker, Geraint, Komjathy, Attila, and Lazio, T. Joseph W.,. Tue . "The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages". United States. https://doi.org/10.3847/0004-637X/831/1/6.
@article{osti_22868558,
title = {The effects of the ionosphere on ground-based detection of the global 21 cm signal from the cosmic dawn and the dark ages},
author = {Datta, Abhirup and Burns, Jack O. and Bradley, Richard and Harker, Geraint and Komjathy, Attila and Lazio, T. Joseph W.,},
abstractNote = {Detection of the global H i 21 cm signal from the Cosmic Dawn and the Epoch of Reionization is the key science driver for several ongoing ground-based and future ground-/space-based experiments. The crucial spectral features in the global 21 cm signal (turning points) occur at low radio frequencies ≲100 MHz. In addition to the human-generated radio frequency interference, Earth’s ionosphere drastically corrupts low-frequency radio observations from the ground. In this paper, we examine the effects of time-varying ionospheric refraction, absorption, and thermal emission at these low radio frequencies and their combined effect on any ground-based global 21 cm experiment. It should be noted that this is the first study of the effect of a dynamic ionosphere on global 21 cm experiments. The fluctuations in the ionosphere are influenced by solar activity with flicker noise characteristics. The same characteristics are reflected in the ionospheric corruption to any radio signal passing through the ionosphere. As a result, any ground-based observations of the faint global 21 cm signal are corrupted by flicker noise (or 1/f noise, where f is the dynamical frequency) which scales as ν{sup −2} (where ν is the frequency of radio observation) in the presence of a bright galactic foreground (∝ν{sup −s}, where s is the radio spectral index). Hence, the calibration of the ionosphere for any such experiment is critical. Any attempt to calibrate the ionospheric effects will be subject to the inaccuracies in the current ionospheric measurements using Global Positioning System (GPS) ionospheric measurements, riometer measurements, ionospheric soundings, etc. Even considering an optimistic improvement in the accuracy of GPS–total electron content measurements, we conclude that Earth’s ionosphere poses a significant challenge in the absolute detection of the global 21 cm signal below 100 MHz.},
doi = {10.3847/0004-637X/831/1/6},
url = {https://www.osti.gov/biblio/22868558}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 831,
place = {United States},
year = {2016},
month = {11}
}