Fermi-LAT Discovery of Extended Gamma-ray Emission in the Direction of Supernova Remnant W51C

Understand

The discovery of bright gamma-ray emission coincident with supernova remnant (SNR) W51C is reported using the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope.

• W51C is a middle-aged remnant (~10^4 yr) with intense radio synchrotron emission in its shell and known to be interacting with a molecular cloud.
• The gamma-ray emission is spatially extended, broadly consistent with the radio and X-ray extent of SNR W51C.
• The energy spectrum in the 0.2-50 GeV band exhibits steepening toward high energies.