Characterization of the gamma-ray emission from the Kepler supernova remnant with Fermi-LAT

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 gamma-ray candidate in the direction of the SNR. Using approximately the same data set but with an optimized analysis configuration, we confirm the gamma-ray candidate to a solid >6 sigma 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 gamma-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 gamma rays through pi degrees decay. The X-ray synchrotron and inverse-Compton emission mostly stem from the fast shocks in the southern regions with a magnetic field B similar to 100 mu G or higher. Depending on the exact magnetic field amplitude, the TeV gamma-ray emission could arise from either the south region (inverse-Compton dominated) or the interaction region (pi degrees decay dominated).