Anisotropy in the Microwave Sky: Results from the First Flight of BAM

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Results are reported from the first flight of a new balloon-borne instrument, BAM (Balloon-borne Anisotropy Measurement), designed to search for cosmic microwave background (CMB) anisotropy. The instrument uses a cryogenic differential Fourier transform spectrometer to obtain data in five spectral channels whose central frequencies lie in the range 3.7 cm⁻¹ to 8.5 cm⁻¹. The spectrometer is coupled to an off-axis prime focus telescope; the combination yields difference spectra of two regions on the sky defined by 0 7 FWHM beams separated by 3 6. Single differences obtained at ten sky positions show statistically significant fluctuations. Assuming Gaussian correlated anisotropy, for the band average 3.1 cm⁻¹ to 9.2 cm⁻¹, one finds ΔT/T = 3.1⁺³.¹₁.₁× 10⁻⁵ (90% confidence interval) for a correlation angle of 1 2. This corresponds to Qflat = 35.9¹⁷.⁷₆.₃ μK (1σ).