Needlet bispectrum asymmetries in the WMAP 5-year data

We apply the needlet formalism to the Wilkinson Microwave Anisotropy Probe 5-year data, looking for evidence of non-Gaussianity in the bispectrum of the needlet amplitudes. We confirm earlier findings of an asymmetry in the non-Gaussianity between the Northern and Southern Galactic hemispheres. We attempt to isolate which scales and geometrical configurations are most anomalous and find that the bispectrum is most significant on large scales and in the more co-linear configurations and also in the ‘squeezed’ configurations. However, these anomalies do not appear to affect the estimate of the non-linear parameter fNL, and we see no significant difference between its values measured in the two hemispheres.