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Precision measurement of the scalar perturbation spectral index, n_s, fromthe Wilkinson Microwave Anisotropy Probe temperature angular power spectrumrequires the subtraction of unresolved point source power. Here we reconsiderthis issue. First, we note a peculiarity in the WMAP temperature likelihood'sresponse to the source correction: Cosmological parameters do not respond toincreased source errors. An alternative and more direct method for treatingthis error term acts more sensibly, and also shifts n_s by ~0.3 sigma closer tounity. Second, we re-examine the source fit used to correct the power spectrum.This fit depends strongly on the galactic cut and the weighting of the map,indicating that either the source population or masking procedure is notisotropic. Jackknife tests appear inconsistent, causing us to assign largeuncertainties to account for possible systematics. Third, we note that the WMAPteam's spectrum was computed with two different weighting schemes: uniformweights transition to inverse noise variance weights at l = 500. The fitdepends on such weighting schemes, so different corrections apply to eachmultipole range. For the Kp2 mask used in cosmological analysis, we prefersource corrections A = 0.012 +/- 0.005 muK^2 for uniform weighting and A =0.015 +/- 0.005 muK^2 for N_obs weighting. Correcting WMAP's spectrumcorrespondingly, we compute cosmological parameters with our alternativelikelihood, finding n_s = 0.970 +/- 0.017 and sigma_8 = 0.778 +/- 0.045 . Thisn_s is only 1.8 sigma from unity, compared to the ~2.6 sigma WMAP 3-yearresult. Finally, an anomalous feature in the source spectrum at l<200 remains,most strongly associated with W-band.

The scalar perturbation spectral index n_s: WMAP sensitivity to unresolved point sources