Measuring the global 21-cm signal with the MWA-I: Improved measurements of the Galactic synchrotron background using lunar occultation

B. McKinley, G. Bernardi, C. M. Trott, J. L.B. Line, R. B. Wayth, A. R. Offringa, B. Pindor, C. H. Jordan, M. Sokolowski, S. J. Tingay, E. Lenc, N. Hurley-Walker, Judd Bowman, F. Briggs, R. L. Webster

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

We present early results from a project to measure the sky-averaged (global), redshifted 21 cm signal from the Epoch of Reionization (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially invariant global average, they cannot be used to detect this signal using standard techniques.However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper, we present one night of Moon observations with the MWA between 72-230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moon's flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected 'earthshine' and by employing image differencing to remove imaging artefacts. We leave the Moon's (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure Tmoon = 180 ± 12 K and a Galactic synchrotron spectral index of -2.64 ± 0.14, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA.

Original languageEnglish (US)
Pages (from-to)5034-5045
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume481
Issue number4
DOIs
StatePublished - Dec 1 2018

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lunar occultation
moon
Moon
synchrotrons
sky
brightness temperature
time measurement
radio
interferometer
night
artifact
artifacts
interferometers
flux density
measuring
telescopes

Keywords

  • Dark ages
  • First stars
  • Moon
  • Reionization
  • Techniques: interferometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Measuring the global 21-cm signal with the MWA-I : Improved measurements of the Galactic synchrotron background using lunar occultation. / McKinley, B.; Bernardi, G.; Trott, C. M.; Line, J. L.B.; Wayth, R. B.; Offringa, A. R.; Pindor, B.; Jordan, C. H.; Sokolowski, M.; Tingay, S. J.; Lenc, E.; Hurley-Walker, N.; Bowman, Judd; Briggs, F.; Webster, R. L.

In: Monthly Notices of the Royal Astronomical Society, Vol. 481, No. 4, 01.12.2018, p. 5034-5045.

Research output: Contribution to journalArticle

McKinley, B, Bernardi, G, Trott, CM, Line, JLB, Wayth, RB, Offringa, AR, Pindor, B, Jordan, CH, Sokolowski, M, Tingay, SJ, Lenc, E, Hurley-Walker, N, Bowman, J, Briggs, F & Webster, RL 2018, 'Measuring the global 21-cm signal with the MWA-I: Improved measurements of the Galactic synchrotron background using lunar occultation', Monthly Notices of the Royal Astronomical Society, vol. 481, no. 4, pp. 5034-5045. https://doi.org/10.1093/MNRAS/STY2437
McKinley, B. ; Bernardi, G. ; Trott, C. M. ; Line, J. L.B. ; Wayth, R. B. ; Offringa, A. R. ; Pindor, B. ; Jordan, C. H. ; Sokolowski, M. ; Tingay, S. J. ; Lenc, E. ; Hurley-Walker, N. ; Bowman, Judd ; Briggs, F. ; Webster, R. L. / Measuring the global 21-cm signal with the MWA-I : Improved measurements of the Galactic synchrotron background using lunar occultation. In: Monthly Notices of the Royal Astronomical Society. 2018 ; Vol. 481, No. 4. pp. 5034-5045.
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abstract = "We present early results from a project to measure the sky-averaged (global), redshifted 21 cm signal from the Epoch of Reionization (EoR), using the Murchison Widefield Array (MWA) telescope. Because interferometers are not sensitive to a spatially invariant global average, they cannot be used to detect this signal using standard techniques.However, lunar occultation of the radio sky imprints a spatial structure on the global signal, allowing us to measure the average brightness temperature of the patch of sky immediately surrounding the Moon. In this paper, we present one night of Moon observations with the MWA between 72-230 MHz and verify our techniques to extract the background sky temperature from measurements of the Moon's flux density. We improve upon previous work using the lunar occultation technique by using a more sophisticated model for reflected 'earthshine' and by employing image differencing to remove imaging artefacts. We leave the Moon's (constant) radio brightness temperature as a free parameter in our fit to the data and as a result, measure Tmoon = 180 ± 12 K and a Galactic synchrotron spectral index of -2.64 ± 0.14, at the position of the Moon. Finally, we evaluate the prospects of the lunar occultation technique for a global EoR detection and map out a way forward for future work with the MWA.",
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AU - McKinley, B.

AU - Bernardi, G.

AU - Trott, C. M.

AU - Line, J. L.B.

AU - Wayth, R. B.

AU - Offringa, A. R.

AU - Pindor, B.

AU - Jordan, C. H.

AU - Sokolowski, M.

AU - Tingay, S. J.

AU - Lenc, E.

AU - Hurley-Walker, N.

AU - Bowman, Judd

AU - Briggs, F.

AU - Webster, R. L.

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