The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales .
We analyze the angular power spectrum of the diffuse emission measured by the Fermi LAT at Galactic latitudes |b| > 30 ^ { \circ } in four energy bins spanning 1 to 50 GeV .
At multipoles \ell \geq 155 , corresponding to angular scales \lesssim 2 ^ { \circ } , angular power above the photon noise level is detected at > 99.99 % CL in the 1–2 GeV , 2–5 GeV , and 5–10 GeV energy bins , and at > 99 % CL at 10–50 GeV .
Within each energy bin the measured angular power takes approximately the same value at all multipoles \ell \geq 155 , suggesting that it originates from the contribution of one or more unclustered source populations .
The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies , C _ { P } / \langle I \rangle ^ { 2 } = 9.05 \pm 0.84 \times 10 ^ { -6 } sr , while the energy dependence of C _ { P } is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index \Gamma _ { s } = 2.40 \pm 0.07 .
We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background .