Nonthermal GeV emission from the Nereides nebula: Confirming the nature of the supernova remnant G107.7-5.1

Context. Recently, the Nereides nebula was discovered through deep optical emission line observations and was classified as a supernova remnant (SNR) candidate, G107.7-5.1. Aims. Since very little is known about this SNR, we have looked at several archival datasets to better understand the environment and properties of the object. Methods. We present a detailed analysis of the gamma-ray emission detected by the Fermi Large Area Telescope in the region of the nebula. A model of the nonthermal emission is presented that allows us to derive the particle distribution responsible for the gamma rays. We also use molecular gas and atomic hydrogen observations to try to constrain the source age and distance. Results. An extended (similar to 2 degrees) GeV source coincident with the location of the nebula is found. The nonthermal emission has a hard spectrum and is detected up to similar to 100 GeV, confirming the SNR nature of this object. The GeV properties of G107.7-5.1 are similar to those of other SNRs such as G150.3 + 4.5, and it likely expands in a relatively low-density medium. The Nereides nebula is one more example of a growing population of dim SNRs detected at high energies. A simple leptonic model is able to account for the gamma-ray emission. Standard SNR evolutionary models constrain the age to be in the 10 - 50 kyr range, which is consistent with estimates of the maximum particle energy obtained from GeV observations. However, more detailed observations of the source should be carried out to better understand its properties.