Improved measurement of the spectral index of the diffuse radio background between 90 and 190 MHz

T. J. Mozdzen, Judd Bowman, R. A. Monsalve, A. E E Rogers

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47 Scopus citations


We report absolutely calibrated measurements of diffuse radio emission between 90 and 190MHzfrom the Experiment to Detect the Global EoR Signature (EDGES). EDGESemploys 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 211 nights of data acquired from 2015 July to 2016 March.We derive the spectral index, β, as a function of local sidereal time (LST) and find -2.60 > β > -2.62 ± 0.02 between 0 and 12 h LST. When the Galactic Centre is in the sky, the spectral index flattens, reaching β = -2.50 ± 0.02 at 17.7 h. The EDGES instrument is shown to be very stable throughout the observations with night-to-night reproducibility of σ β < 0.003. Including systematic uncertainty, the overall uncertainty of β is 0.02 across all LST bins. These results improve on the earlier findings of Rogers & Bowman by reducing the spectral index uncertainty from 0.10 to 0.02 while considering more extensive sources of errors. We compare our measurements with spectral index simulations derived from the Global Sky Model (GSM) of de Oliveira- Costa et al. and with fits between the Guzmán et al. 45MHz and Haslam et al. 408 MHz maps. We find good agreement at the transit of the Galactic Centre. Away from transit, the GSM tends to overpredict (GSM less negative) by 0.05 < Δ β = βGSM - βEDGES < 0.12, while the 45-408 MHz fits tend to overpredict by Δβ < 0.05.

Original languageEnglish (US)
Pages (from-to)4995-5002
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
StatePublished - Feb 1 2017


  • Dark ages
  • First stars
  • Galaxy: structure
  • Instrumentation: miscellaneous
  • Reionization

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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