Absorption of curvature radiation

The reabsorption of curvature radiation, i.e. radiation from relativistic electrons moving along curved magnetic field lines, is discussed. The optical depth for the ray path is calculated by use of the Einstein coefficients. It is shown that the optical depth becomes negative (maser effect) if transitions between Landau levels are absent. However, maser action is ineffective if the energy density of the relativistic particles is less than that of the magnetic field. For pulsar radio emission the magnetic energy density is assumed to exceed the particle energy density, so the observed emission cannot be coherent curvature radiation