Multifrequency Radio Observations of the Crab Pulsar
  Previously unseen profile components of the Crab pulsar have been discovered in a study of the frequency-dependent behavior of its average pulse profile between 0.33 and 8.4 GHz. One new component, 36 degrees ahead of the main pulse at 1.4 GHz, is not coincident with the position of the precursor at lower frequencies. Two additional, flat-spectrum components appear after the interpulse between 1.4 and 8.4 GHz. The normal interpulse undergoes a transition in phase and spectrum by disappearing near 2.7 GHz, and reappearing 10 degrees earlier in phase at 4.8 and 8.4 GHz with a new spectral index. The radio frequency main disappears for frequencies above 4.8 GHz, even though it is seen at infrared, optical, and higher energies. The existence of the additional components at high frequency and the strange, frequency-dependent behavior is unlike anything seen in other pulsars, and cannot easily be explained by emission from a simple dipole field geometry. 
D.A.Moffett, T.H.Hankins (New Mexico Tech)