  G279.0+1.1 is a supernova remnant (SNR) with poorly known parameters, first
detected as a dim radio source and classified as an evolved system. An analysis
of data from the Fermi-LAT revealing for the first time an extended source of
gamma rays in the region is presented. The diameter of the GeV region found is
~2.8$^{\circ}$, larger than the latest estimate of the SNR size from radio
data. The gamma-ray emission covers most of the known shell and extends further
to the north and east of the bulk of the radio emission. The photon spectrum in
the 0.5--500 GeV range can be described by a simple power law, $\frac{dN}{dE}
\propto E^{-\Gamma}$, with a spectral index of $\Gamma = 1.86\pm 0.03_{stat}
\pm 0.06_{sys}$. In the leptonic scenario, a steep particle spectrum is
required and a distance lower than the previously estimated value of 3 kpc is
favored. The possibility that the high-energy emission results from electrons
that already escaped the SNR is also investigated. A hadronic scenario for the
gamma rays yields a particle spectral index of $\sim2.0$ and no significant
constraints on the distance. The production of gamma rays in old SNRs is
discussed. More observations of this source are encouraged to probe the true
extent of the shell and its age.
