On the theory of cyclotron absorption at the wing of the absorption line

It is shown that, at the wing of the cyclotron absorption line, the relativistic effects associated with the dependence of the gyrofrequency on the particle energy can play an important role even far from the relativistic cyclotron cutoff region, i.e., even when the resonance lines in velocity space are mainly determined by the nonrelativistic Doppler synchronizm. Simple relationships for the relativistic absorption coefficient and power deposition profile in a nonuniformly magnetized plasma slab, as well as a new condition, which was not discussed earlier, for the applicability of the nonrelativistic approximation, are derived from illustrative physical considerations