(Nicolao Fornengo, Marco Regis and Simone Ammazzalorso)
The exact composition of the gamma-ray sky is still an open question in gamma-ray astrophysics. The unresolved gamma-ray background (UGRB) may represent the only available information about sources (astrophysical or exotic, like dark matter) too faint to be detected individually. The Fermi-LAT telescope, with its superior performance, enables us to perform an energy-resolved autocorrelation analysis of the spatial distribution of UGRB intensity fluctuations, for which we devised a new technique preventing the random noise field to affect the result of our analysis. For the first time we find clear evidence that two spectrally different source classes contribute to the UGRB. Here we provide details about the analysis and comment on possible interpretations of the result.