TY - JOUR
T1 - Spectral index of the diffuse radio background between 50 and 100 MHz
AU - Mozdzen, T. J.
AU - Mahesh, N.
AU - Monsalve, R. A.
AU - Rogers, A. E.E.
AU - Bowman, Judd
N1 - Funding Information:
This work was supported by the NSF through research awards for the Experiment to Detect the Global EoR Signature (AST-1207761 and AST-1609450). RAM was supported by the NASA Solar System Exploration Virtual Institute cooperative agreement 80ARC017M0006 and by the NASA Ames Research Center grant NNX16AF59G. EDGES is located at the Murchison Radioastronomy Observatory. We acknowledge the Wajarri Yamatji people as the traditional owners of the Observatory site. We thank CSIRO for providing site infrastructure and support.
Publisher Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.
PY - 2019/3/11
Y1 - 2019/3/11
N2 - We report the spectral index of diffuse radio emission between 50 and 100 MHz from data collected with two implementations of the Experiment to Detect the Global EoR Signature (EDGES) low-band system. EDGES employs a wide-beam zenith-pointing dipole antenna centred on a declination of -26.7°. We measure the sky brightness temperature as a function of frequency averaged over the EDGES beam from 244 nights of data acquired between 2016 September 14 and 2017 August 27. We derive the spectral index, β, as a function of local sidereal time (LST) using night-time data and a two-parameter fitting equation. We find -2.59 < β < -2.54 ± 0.011 between 0 and 12 h LST, ignoring ionospheric effects. When the Galactic Centre is in the sky, the spectral index flattens, reaching β = -2.46 ± 0.011 at 18.2 h. The measurements are stable throughout the observations with night-to-night reproducibility of σ β < 0.004 except for the LST range of 7 to 12 h. We compare our measurements with predictions from various global sky models and find that the closest match is with the spectral index derived from the Guzmán and Haslam sky maps, similar to the results found with the EDGES high-band instrument for 90-190 MHz. Three-parameter fitting was also evaluated with the result that the spectral index becomes more negative by ~0.02 and has a maximum total uncertainty of 0.016. We also find that the third parameter, the spectral index curvature, γ, is constrained to -0.11 < γ < -0.04. Correcting for expected levels of night-time ionospheric absorption causes β to become more negative by 0.008-0.016 depending on LST.
AB - We report the spectral index of diffuse radio emission between 50 and 100 MHz from data collected with two implementations of the Experiment to Detect the Global EoR Signature (EDGES) low-band system. EDGES employs a wide-beam zenith-pointing dipole antenna centred on a declination of -26.7°. We measure the sky brightness temperature as a function of frequency averaged over the EDGES beam from 244 nights of data acquired between 2016 September 14 and 2017 August 27. We derive the spectral index, β, as a function of local sidereal time (LST) using night-time data and a two-parameter fitting equation. We find -2.59 < β < -2.54 ± 0.011 between 0 and 12 h LST, ignoring ionospheric effects. When the Galactic Centre is in the sky, the spectral index flattens, reaching β = -2.46 ± 0.011 at 18.2 h. The measurements are stable throughout the observations with night-to-night reproducibility of σ β < 0.004 except for the LST range of 7 to 12 h. We compare our measurements with predictions from various global sky models and find that the closest match is with the spectral index derived from the Guzmán and Haslam sky maps, similar to the results found with the EDGES high-band instrument for 90-190 MHz. Three-parameter fitting was also evaluated with the result that the spectral index becomes more negative by ~0.02 and has a maximum total uncertainty of 0.016. We also find that the third parameter, the spectral index curvature, γ, is constrained to -0.11 < γ < -0.04. Correcting for expected levels of night-time ionospheric absorption causes β to become more negative by 0.008-0.016 depending on LST.
KW - Galaxy: structure
KW - Instrumentation:miscellaneous
KW - dark ages, reionisation, first stars
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U2 - 10.1093/mnras/sty3410
DO - 10.1093/mnras/sty3410
M3 - Article
AN - SCOPUS:85062281703
SN - 0035-8711
VL - 483
SP - 4416
EP - 4428
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 4
ER -