The Non‐Gaussian Cold Spot in the 3 YearWilkinson Microwave Anisotropy ProbeData

The non-Gaussian cold spot detected in wavelet space in the WMAP 1-year data,is detected again in the coadded WMAP 3-year data at the same position (b =-57, l = 209) and size in the sky (around 10 degrees). The present analysis isbased on several statistical methods: kurtosis, maximum absolute temperature,number of pixels below a given threshold, volume and Higher Criticism. Allthese methods detect deviations from Gaussianity in the 3--year data set at aslightly higher confidence level than in the WMAP 1-year data. These smalldifferences are mainly due to the new foreground reduction technique and not tothe 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-yeardata the significance of the deviation in the kurtosis. The skewness andkurtosis 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 inGaussian simulations is 1.85%. The frequency dependence of the spot is shown tobe extremely flat. Galactic foreground emissions are not likely to beresponsible for the detected deviation from Gaussianity.Comment: New section on significance, considering only a priori statistics. Accepted for publication in Ap