Angular power spectrum of the cosmic microwave background anisotropy seen by the COBE DMR

The angular power spectrum estimator developed by Peebles and Hauser & Peebles has been modified and applied to the 4 yr maps produced by the COBE DMR. The power spectrum of the observed 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). The best-fitting value of the spectral index in the range of spatial scales corresponding to spherical harmonic indices 3 less than or equal to l less than or similar to 30 is an apparent spectral index n(app) = 1.13(-0.4)(+0.3) which is consistent with the Harrison-Zeldovich primordial spectral index n(pri) = 1. The best-fitting amplitude for n(app) = 1 is [Q(rms)(2)](0.5) = 18 mu K.