The superluminal spectral densities of relativistic electrons in uniform motion are derived, semiclassically and in second quantization. The effect of electron spin on the tachyonic radiation field, a Proca field with negative mass-square, is studied. There is a longitudinally polarized spectral component due to the negative mass-square of the tachyonic quanta. The radiation densities are averaged with electron distributions, and high- and low-temperature expansions are obtained. Spectral fits to the γ-ray spectra of the Crab Nebula, the supernova remnant RX J1713.7–3946, and the BL Lacertae objects H1426+428, 1ES 1959+650, Mkn 501, and Mkn 421 are performed. In contrast to TeV photons, the extragalactic tachyon flux is not attenuated by interaction with the background light; there is no absorption of tachyonic γ-rays, as tachyons do not interact with infrared photons. The curvature of the TeV spectra in double-logarithmic plots is caused by the Boltzmann factor of the electron densities generating the tachyon flux. The extended spectral plateau in the GeV band, visible in the spectral maps of the two Galactic supernova remnants as well as in the flare spectra of the BL Lacertae objects, is reproduced by the tachyonic radiation densities. Estimates of the electron populations in the supernova remnants and active galactic nuclei are inferred from the spectral fits, such as power-law indices, electron temperatures, and source counts. Upper bounds on the Lorentz factors in the source populations are derived and compared to the breaks in the high-energy cosmic-ray spectrum.