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

Abstract

We report the discovery of a $\sim$ $3.4\degr$-wide region of high-energy emission in data from the \emph{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$\degr$, b=-4.7$\degr$. It shows a hard spectrum that is compatible with a simple power-law, $\frac{dN}{dE}\propto E^{-\Gamma}$, in the energy range 0.7--500 GeV, with a spectral index $\Gamma = 1.68 \pm 0.04_{\mbox{stat}} \pm 0.1_{\mbox{sys}}$. The integrated source photon flux above 0.7 GeV is $(4.71 \pm 0.49_{\mbox{stat}}\pm 2.13_{\mbox{sys}}) \times 10^{-9}$ 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.