The Spectrum of Low Radio Frequency Background Radiation

Abstract

Abstract The paper describes measurements of sky brightness temperatures at frequencies of 38 Mc/s, 26.5 Mc/s, 17.5 Mc/s, 13.1 Mc/s, and 10 Mc/s using dipoles centred on δ = 52°. The frequency spectrum of the radiation originating in the region of the galactic halo is derived from these measurements by plotting the temperatures at the four lower frequencies against the corresponding temperatures at 38 Mc/s. Combining this with a previous determination of the spectrum at higher frequencies by Purton enables the spectrum of the flux of radiation from the galactic halo to be established in the frequency range 404–10 Mc/s. The spectrum is straight, with a spectral index α = 0.43±0.03, over the range 178–10 Mc/s, though slight curvature could also be possible within the experimental accuracy. This implies that the energy spectrum of the cosmic ray electrons which are the source of the radiation has a value of γ ∼ 1.85 in the approximate energy range 10 9 –5 × 10 9 eV.