AN ESTIMATE OF THE COBE QUADRUPOLE

Bennett et al. and Smoot et al- reported in 1992 the first positive measurement of the fluctuations in the cosmic microwave background, including a 3 sigma detection of the quadrupole, Q(rms) = 13 +/- 4 uK (as inferred from the individual quadrupole components in the ''combination'' and ''reduced galaxy'' Absolute value of b > 10-degrees maps). I show that part of the observed fluctuations are actually due to noise, so that the best estimate of Q(rms) in these maps is 10.5 muK. This estimate of Q(rms) is substantially below the value Q(rms-PS) approximately 16 muk predicted for the quadrupole by extrapolating to l = 2, the observed power-spectrum index (n = 1.1), from higher multipole moments. This reduced estimate of the quadrupole helps explains why the best fit to the spectral index steepens to n = 1.5 when the quadrupole is included in the fit.