Authors:聽T.J. Mozdzen, J.D. Bowman, R.A. Monsalve, A.E.E. Rogers
Abstract:聽We report absolutely calibrated measurements of diffuse radio emission between 90 and 190 MHz from the Experiment to Detect the Global EoR Signature (EDGES). EDGES employs a wide beam zenith-pointing dipole antenna centred on a declination of 鈭�26.7鈼�. 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, 尾, as a function of local sidereal time (LST) and find 鈭�2.60 > 尾 > 鈭�2.62 卤 0.02 between 0 and 12 h LST. When the Galactic Centre is in the sky, the spectral index flattens, reaching 尾 = 鈭�2.50 卤 0.02 at 17.7 h. The EDGES instrument is shown to be very stable throughout the observations with night-to-night reproducibility of 蟽尾 < 0.003. Including systematic uncertainty, the overall uncertainty of 尾 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 Guzma 虂n et al. 45 MHz 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 < 聽螖尾 = 尾GSM 鈭� 尾EDGES < 0.12, while the 45鈥�408 MHz fits tend to overpredict by聽螖尾 < 0.05.