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

Abstract

We propose the synchrotron self-Compton (SSC) scenario coupled with filamentary jet model, to reproduce the very high energy $\gamma$-ray emissions from Cen A. With reference to self-similarity of knot-like features in the jet, we assume nonuniform magnetic field associated with current filaments having various transverse sizes. For energetic electron production, the diffusive shock acceleration at sites distributed over the kiloparsec-scale jet is considered. We show that maximum Lorentz factor of the electron steadily exceeds $10^{8}$ due to suppression of synchrotron loss of the electrons trapped in weak magnetic field of the thin filaments, and inhomogeneous SSC in the inner jet can dominantly contribute to establishment of the pronounced hardening of $\gamma$-ray flux detected by the 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.