ANGULAR POWER SPECTRUM OF THE MICROWAVE BACKGROUND ANISOTROPY SEEN BY THE COBE DIFFERENTIAL MICROWAVE RADIOMETER

The angular power spectrum estimator developed by Peebles (1973) and Hauser and Peebles (1973) has been modified and applied to the 2 yr maps produced by the COBE DMR. The power spectrum of the real sky has been compared to the power spectra of a large number of simulated random skies produced with noise equal to the observed noise and primordial density fluctuation power spectra of power-law form, with P(k) proportional to k(n). Within the limited range of spatial scales covered by the COBE DMR, corresponding to spherical harmonic indices 3 less than or equal to l less than or similar to 30, the best-fitting value of the spectral index is n = 1.25(-0.45)(+0.4) with the Harrison-Zel'dovich value n = 1 approximately 0.5 sigma below the best fit. For 3 less than or equal to l less than or similar to 19, the best fit is n = 1.46(-0.44)(+0.39). Comparing the COBE DMR Delta T/T at small l to the Delta T/T at 1 approximate to 50 from degree scale anisotropy experiments gives a smaller range of acceptable spectral indices which includes n = 1.