AN ESTIMATE OF THE PRIMORDIAL NON-GAUSSIANITY PARAMETER fNL USING THE NEEDLET BISPECTRUM FROM WMAP

We use the full bispectrum of spherical needlets applied to the WMAP data of the cosmic microwave background as an estimator for the primordial non-Gaussianity parameter f(NL). We use needlet scales up to l(max) = 1000 and the KQ75 galactic cut and find f(NL) = 84 +/- 40 corrected for point-source bias. We also introduce a set of consistency tests to validate our results against the possible influence of foreground residuals or systematic errors. In particular, fluctuations in the value of f(NL) obtained from different frequency channels, different masks, and different multipoles are tested against simulated maps. All variations in f(NL) estimates are found statistically consistent with simulations.