High Energy Radiation Generated at Boundary Shear Layers of Relativistic Jets

A simple model of cosmic ray electron acceleration at the jet boundary yields a power law particle energy distribution of ultra-relativistic electrons with an energy cut-off growing with time, and, finally, a growing particle bump at the energy where energy gains equal radiation losses. For such electron distribution, in tens-of-kpc scale jets, we derived the observed time-varying spectra of synchrotron and inverse Compton radiation, including Comptonisation of synchrotron and cosmic microwave background photons. Slowly varying spectral index along the jet in the `low frequency' spectral range is a natural consequence of boundary layer acceleration. Variations of the high energy bump of the electron distribution can give rise to anomalous behaviour in the X-ray band in comparison to the lower frequencies.