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 language | English (US) |
|---|---|
| Pages (from-to) | 5034-5045 |
| Number of pages | 12 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 481 |
| Issue number | 4 |
| DOIs | |
| State | Published - Dec 1 2018 |
Fingerprint
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 journal › Article
}
TY - JOUR
T1 - Measuring the global 21-cm signal with the MWA-I
T2 - Improved measurements of the Galactic synchrotron background using lunar occultation
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.
PY - 2018/12/1
Y1 - 2018/12/1
N2 - 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.
AB - 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.
KW - Dark ages
KW - First stars
KW - Moon
KW - Reionization
KW - Techniques: interferometric
UR - http://www.scopus.com/inward/record.url?scp=85060909021&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85060909021&partnerID=8YFLogxK
U2 - 10.1093/MNRAS/STY2437
DO - 10.1093/MNRAS/STY2437
M3 - Article
AN - SCOPUS:85060909021
VL - 481
SP - 5034
EP - 5045
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
SN - 0035-8711
IS - 4
ER -