Characterization of the Gamma-ray Emission from the Kepler Supernova Remnant with Fermi-LAT

¹ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif- sur- Yvette, France
e-mail: fabio.acero@cea.fr
² Univ. Bordeaux, CNRS, LP2I Bordeaux, UMR 5797, 33170 Gradignan, France

Received: 10 September 2021
Accepted: 8 January 2022

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 >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 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).