A measurement of the anisotropy in the cosmic microwave background radiation at degree angular scales

We detect anisotropy in celestial radiation at degree angular scales between 26 and 36 GHz. The fluctuations have the spectral index of the cosmic microwave background radiation. The rms amplitude, Δ_rms, of the fluctuations in the data set is 33_-9⁺¹⁰ μK, and the average spectral index, β, is -0.3_-1.2^+0.7; for the cosmic microwave background, β = 0. The 95% confidence upper limit on the anisotropy of the polarization is 25 μK. The most likely amplitude of a Gaussian correlation function, a scan- and beam-independent measure of the fluctuations, is 41_-13⁺¹⁶ μK with β = -0.3_-1.2^+0.7 at a coherence angle of 1°.2. At these frequencies, some fraction of Δ_rms is probably due to anisotropy in free-free emission (β = -2.1), but our bounds on the spectral index argue that the free-free contribution is not large. Known compact sources and synchrotron radiation do not contribute substantially to the detected anisotropy.