Characterization of the Gamma-ray Emission from the <i>Kepler</i> Supernova Remnant with <i>Fermi-LAT</i>
F. Acero, M. Lemoine‐Goumard, J. Ballet
Abstract
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 >6 σ 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 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).