Origin of electrons and steep spectrum in filaments connecting 3C 84 to the northwestern ghost cavity

Explain the origin of the radio-emitting electrons and the steep radio spectrum (spectral index approximately −1.5 to −2.0 between 144 and 352 MHz) in the filaments linking 3C 84 to the northwestern X-ray ghost cavity, including whether these electrons are re-accelerated fossil populations or produced by other mechanisms.

Background

In high-resolution LOFAR images, multiple filaments and finer fibers connect 3C 84 to the northwestern ghost cavity with steep spectra. Despite proposing field amplification by AGN outflows, the authors acknowledge that the electron origin and spectral steepness are not well understood.