Abstract
The polarization of superluminal radiation is studied, based on the tachyonic Maxwell equations for Proca fields with negative mass-square. The cross-sections for the scattering of transversal and longitudinal tachyons by electrons are derived. The polarized superluminal flux vectors of dipole currents are calculated, and the power transversally and longitudinally radiated is obtained. Specifically, the polarization of the γ-ray spectrum of quasar 3C 279 is studied. Two flare spectra of this blazar at redshift 0.538 are fitted with tachyonic cascades generated by the thermal electron plasma in the active galactic nucleus. The transversal and longitudinal radiation components and the thermodynamic parameters of the ultra-relativistic plasma are extracted from the spectral map. An extended spectral plateau typical for tachyonic γ-ray spectra emerges in the MeV and low GeV range. The curvature of the adjacent GeV spectral slope is shown to be intrinsic, caused by the Boltzmann factor of the electron plasma rather than by intergalactic absorption.