2022A&A...660A.129A

The Kepler supernova remnant (SNR) had been the only historic SNR that lacked a detection at GeV and TeV energies, which probe particle acceleration. A recent analysis of Fermi-LAT data reported a likely GeV γ-ray candidate in the direction of the SNR. Using approximately the same data set but with an optimized analysis configuration, we confirm the γ-ray candidate to a solid >6σ detection and report a spectral index of 2.14 ± 0.12_stat ± 0.15_syst for an energy flux above 100 MeV of (3.1 ± 0.6_stat ± 0.3_syst) x 10^–12 erg cm^–2 s^–1. The γ-ray excess is not significantly extended and is fully compatible with the radio, infrared, and X-ray spatial distribution of the SNR. We successfully characterized this multiwavelength emission with a model in which accelerated particles interact with the dense circumstellar material in the northwest portion of the SNR and radiate GeV γ rays through π° decay. The X-ray synchrotron and inverse-Compton emission mostly stem from the fast shocks in the southern regions with a magnetic field B ∼ 100 µG or higher. Depending on the exact magnetic field amplitude, the TeV γ-ray emission could arise from either the south region (inverse-Compton dominated) or the interaction region (π° decay dominated).