On the GeV excess in the diffuse γ-ray emission towards the Galactic centre

Abstract

Aims. The Fermi-LAT γ-ray data have been used to study the morphological and spectral features of the so-called GeV excess - a diffuse radiation component recently discovered towards the Galactic centre. Methods. We used the likelihood method to analyze Fermi-LAT data. Our study does confirm the existence of such an extra component in the diffuse γ-ray emission at GeV energies. Based on a detailed morphological analysis, a spatial template that fits the data best was generated and adopted. Results. Using this template, the energy distribution of γ-rays was derived in the 0.3-30 GeV energy interval. The spectrum appeared to have less distinct ("bump"-like) structure than previous reported. We argue that the morphology of this radiation component has a bipolar rather than a spherically symmetric structure as has been assumed a priori in previous studies. Conclusions. This finding excludes the associations of the GeV excess with Dark Matter. We briefly discuss the radiation mechanisms and possible source populations that could be responsible for this new component of diffuse gamma radiation.