We present quantitative statistical evidence for a γ-ray emission halo surrounding the Galaxy. Maps of the emission are derived. EGRET data were analyzed in a wavelet-based non-parametric hypothesis testing framework, using a model of expected diﬀuse (Galactic + isotropic) emission as a null hypothesis. The results show a statistically signiﬁcant large scale halo surrounding the center of the Milky Way as seen from Earth. The halo ﬂux at high latitudes is somewhat smaller than the isotropic γ-ray ﬂux at the same energy, though of the same order (O(10−7–10−6) ph cm−2 s−1 sr−1 above 1 GeV).
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