Origin of Pulsar Radiation

Abstract

THERE have recently been some very interesting developments in the theory of the propagation of electromagnetic waves through resonant media, which may have a bearing on the origin of pulsars^1–3. Theories of anomalous dispersion usually assume that the resonant systems can be regarded as harmonic oscillators. This is already an approximation, for most transitions in atomic systems involve precisely two energy levels—upper and lower—rather than a ladder of equally spaced energy levels which characterizes a harmonic oscillator. The difference is of little consequence when the exciting radiation is weak, but when it is intense theory suggests that there will be striking differences. For example, an incident continuous wave of uniform amplitude may emerge as a succession of equally spaced pulses of radiation. In broad terms, what happens is that an intense wave, on resonance, will take an atom initially in its ground state to its excited state and back down again coherently. In the first part of the cycle, energy is taken from the wave, to be returned to it in the latter part of the cycle. So if the incident wave is of uniform intensity the intensity does not stay uniform as the wave progresses into the resonant medium. The detailed theory, which is as yet incomplete, suggests that the distortion of the wave can be so great that it will emerge as a succession of pulses.