2020MNRAS.492.5980A

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-Large Area Telescope (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°, 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, dN/ dE ∝ E^{-Γ }, with a spectral index of Γ = 1.86 ± 0.03stat ± 0.06sys. In the leptonic scenario, a steep particle spectrum is required and a distance lower than the previously estimated value of 3 kpc is favoured. 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 ∼2.0 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.