The anisotropy in the cosmic microwave background at degree angular scales

We detect anisotropy in the cosmic microwave background (CMB) at degree angular scales and confirm a previous detection reported by Wollack et al. (1993). The root-mean-squared amplitude of the fluctuations is 44_-7⁺¹³ μK. This may be expressed as the square root of the angular power spectrum in a band of multipoles between l_eff = 69_-22⁺²⁹. We find δT_l = [l(2l + 1)〈|a_l^m|²〉/4π]^1/2 = 42_-7⁺¹² μK. The measured spectral index of the fluctuations is consistent with zero, the value expected for the CMB. The spectral index corresponding to Galactic free-free emission, the most likely foreground contaminant, is rejected at ∼ 3 σ. The analysis is based on three independent data sets. The first, taken in 1993, spans the 26-36 GHz frequency range with three frequency bands; the second was taken with the same radiometer as the first but during an independent observing campaign in 1994; and the third, also taken in 1994, spans the 36-46 GHz range in three bands. For each telescope position and radiometer channel, the drifts in the instrument offset are ≤4 μK day^-1 averaged over a period of 1 month. The dependence of the inferred anisotropy on the calibration and data editing is addressed.