Discovery of an extended source of gamma-ray emission in the Southern hemisphere

Abstract

We report the discovery of a ~3°.4-wide region of high-energy emission in data from the Fermi LAT satellite. The centroid of the emission is located in the Southern hemisphere sky, a few degrees away from the plane of the Galaxy at the Galactic coordinates l = 350°.6, b=-4°.7. It shows a hard spectrum that is compatible with a simple power law, dN/dE α E -Λ, in the energy range 0.7-500 GeV, with a spectral index Λ = 1.68 ± 0.04stat ± 0.1sys. The integrated source photon flux above 0.7 GeV is (4.71 ± 0.49stat ± 2.13sys) × 10-9 cm-2 s-1. We discuss several hypotheses for the nature of the source, particularly that the emission comes from the shell of an unknown supernova remnant.