A Measurement of the Angular Power Spectrum of the Anisotropy in the Cosmic Microwave Background

We report on a measurement of the angular power spectrum of the anisotropy inthe Cosmic Microwave Background. The anisotropy is measured in 23 differentmultipole bands from l=54 (~3 deg) to l=404 (~0.45 deg) and in 6 frequencybands from 26 GHz to 46 GHz over three observing seasons. The measurements areconsistent from year to year. The frequency spectral index of the fluctuations(measured at low l) is consistent with that of the CMB and inconsistent witheither dust or Galactic free-free emission. Furthermore, the observations ofthe MSAM1-92 experiment (Cheng et al. 1994) are repeated and confirmed. Theangular spectrum shows a distinct rise from dT_l =\sqrt{l(2l+1)<|a^m_l|^2>/4pi} = 49(+8,-5) \uK at l=87 to dT_l=85(+10,-8) uK atl = 237. These values do not include an overall +/-14\% (1sigma) calibrationuncertainty. The analysis and possible systematic errors are discussed.Comment: latex file is called spect.tex. 25 pages with 11 Postscript figures. Uses aas2pp4.sty (included). Submitted to Ap