Cyclotron and synchrotron radiation of a plasma in superstrong magnetic fields of neutron stars

The cyclotron and synchrotron radiation from a strongly magnetized trans-relativistic electron-positron plasma is investigated on the basis of the quantum relativistic theory. The quantization of the transverse motion of radiating particles leads to sharp asymmetric peaks in the absorption and emission spectral and angular dependence. The peaks arise at n ̵ omega; = mc 2 × (√1+2 n′ b − √1+2 nb)/ sin O , where ω is the photon frequency, O is the angle between the magnetic field and the wave-vector, b = B/4.4×10 13 Gauss, n, n′ = 0, 1, 2, … are the numbers of the Landau levels. The quantum recoil softens the emission spectra. The anharmonicity of the Landau levels leads to a new type of spectral peaks for anisotropic electron-positron distributions with typical transverse momenta exceeding the longitudinal ones. Nonthermal distributions may lead to the maser amplification of the radiation. The maser effects are strictly forbidden for photons propagating along the magnetic field in a tenuous plasma. The considered effects should reveal in radiation of the gamma-ray bursters and X-ray pulsars.