Diffusive synchrotron radiation from extragalactic jets

Flattenings of non-thermal radiation spectra observed from knots and interknot locations of the jets of 3C 273 and M87 in the ultraviolet and X-ray bands are discussed within modern models of magnetic field generation in relativistic jets. Specifically, we explicitly take into account the effect of the small-scale random magnetic field, probably present in such jets, which gives rise to emission of diffusive synchrotron radiation, the spectrum of which deviates substantially from the standard synchrotron spectrum, especially at high frequencies. The calculated spectra agree well with the observed ones if the energy densities contained in small-scale and large-scale magnetic fields are comparable. The implications of this finding for magnetic field generation, particle acceleration and jet composition are discussed.