Characterization of the GeV emission from the Kepler supernova remnant
Abstract
The Kepler supernova remnant (SNR) is the only historic supernova remnant lacking 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 dataset but with an optimized analysis configuration, we confirm the gamma-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) × 10-12 erg~cm-2~s-1. The gamma-ray excess is not significantly extended and is fully compatible with the radio, infrared or X-ray spatial distribution of the SNR. We successfully characterized this multi-wavelength emission with a model in which accelerated particles interact with the dense circumstellar material in the North-West portion of the SNR and radiate GeV gamma-rays through πo decay. The X-ray synchrotron and inverse-Compton (IC) emission mostly stem from the fast shocks in the southern regions with a magnetic field B100 μG or higher. Depending on the exact magnetic field amplitude, the TeV emission could arise from either the South region (IC dominated) or the interaction region (πo decay dominated).