Distributed accelerators in the jet of Centaurus A: Origin of the spectral hardening of very-high-energy gamma-rays

¹ Kindai University Technical College Nabari Mie 518-0459, Japan
² Plasma Astrophysics Laboratory, Institute for Global Science Mie, Japan

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Received: 6 September 2025
Accepted: 16 January 2026

Abstract

We propose the synchrotron self-Compton (SSC) scenario coupled with a filamentary jet model to reproduce the very-high-energy γ-ray emissions from Cen A. With reference to self-similarity of knot-like features in the jet, we assumed a nonuniform magnetic field associated with current filaments of various transverse sizes. For energetic electron production, the diffusive shock acceleration at sites distributed over the kiloparsec-scale jet was considered. We show that the maximum Lorentz factor of the electron steadily exceeds 10⁸ due to suppression of synchrotron loss of the electrons trapped in the weak magnetic field of the thin filaments, and an inhomogeneous SSC scenario in the inner jet can predominantly contribute to establishment of the pronounced hardening of γ-ray flux detected by the High Energy Stereoscopic System (H.E.S.S.). It is also suggested that the spectral contribution from diffuse regions of the outer jet potentially amounts to the observed Fermi fluxes.