BAND POWER SPECTRA IN THE COBE DMR 4-YEAR ANISOTROPY MAPS

We employ a pixel-based likelihood technique to estimate the angular p ower spectrum of the COBE Differential Microwave Radiometer (DMR) 4 yr sky maps. The spectrum is consistent with a scale-invariant power-law form with a normalization, expressed in terms of the expected quadrup ole anisotropy, of Q(rms-PS\n=1) = 18 +/- 1.4 mu K, and a best-fit spe ctral index of 1.2 +/- 0.3. The normalization is somewhat smaller than we concluded from the 2 yr data, mainly due to additional Galactic mo deling. We extend the analysis to investigate the extent to which the ''small'' quadrupole observed in our sky is statistically consistent w ith a power-law spectrum. The most likely quadrupole amplitude ranges between 7 and 10 mu K, depending on the details of Galactic modeling a nd data selection, but in no case is there compelling evidence that th e quadrupole is inconsistent with a power-law spectrum. We conclude wi th a likelihood analysis of the band power amplitude in each of four s pectral bands between l = 2 and 40, and find no evidence for deviation s from a simple power-law spectrum.