The non-Gaussian cold spot in the 3 year Wilkinson Microwave Anisotropy Probe data

The non-Gaussian cold spot detected in wavelet space in the WMAP 1 yr data is detected again in the co-added WMAP 3 yr data at the same position ( b = -57 degrees, l =209 degrees) and size in the sky (approximate to 10 degrees). The present analysis is based on several statistical methods: kurtosis, maximum absolute temperature, number of pixels below a given threshold, volume, and higher criticism. All these methods detect deviations from Gaussianity in the 3 yr data set at a slightly higher confidence level than in the WMAP 1 yr data. These small differences are mainly due to the new foreground reduction technique and not to the reduction of the noise level, which is negligible at the scale of the spot. In order to avoid a posteriori analyses, we recalculate for the WMAP 3 yr data the significance of the deviation in the kurtosis. The skewness and kurtosis tests were the first tests performed with wavelets for the WMAP data. We obtain that the probability of finding an at least as high deviation in Gaussian simulations is 1:85%. The frequency dependence of the spot is shown to be extremely flat. Galactic foreground emissions are not likely to be responsible for the detected deviation from Gaussianity.