Key points are not available for this paper at this time.
The radial locations of a pulsar's emission region are investigated in the context of Radhakrishnan and Cooke's (1969) 'polar cap' or 'plasma flow' model. Corotational velocities are assumed to be secondary, and upper limits are placed on the aberration associated with corotation. Evidence suggesting that different radio frequencies are emitted at different radii is reviewed, and observational consequences of such spatially differentiated emission are considered. Pulsar observations are then used to place constraints on the radii of emission. The results obtained for three pulsars (PSR 0525+21, 0950+08, and 1133+16) are shown to be consistent with either (1) dipolar fields persisting out to a substantial fraction (0.03-0.1) of the light-cylinder radius if actual radii of emission are about equal to their derived upper limits or (2) HF emission occurring at or near the stellar surface and LF emission originating within 10 stellar radii of the surface.
J. M. Cordes (Thu,) studied this question.