Toward an Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights

In this paper we return to the old problem of conal component-pair widths andprofile dimensions. Observationally, we consider a set of 10 pulsars withprominent conal component pairs, for which well measured profiles exist overthe largest frequency range now possible. Apart from some tendency to narrow athigh frequency, the conal components exhibit almost constant widths. We use allthree profile measures, the component separation as well as the outsidehalf-power and 10% widths, to determine conal beam radii, which are the focusof our subsequent analysis. These radii at different frequencies are wellfitted by a relationship introduced by Thorsett (1991), but the resultingparameters are highly correlated. Three different types of behavior are found:one group of stars exhibits a continuous variation of beam radius which can beextrapolated down to the stellar surface along the ``last open field lines''; asecond group exhibits beam radii which asymptotically approach a minimum highfrequency value that is 3--5 times larger; and a third set shows almost nospectral change in beam radius at all. The first two behaviors are associatedwith outer-cone component pairs; whereas the constant separation appears toreflect inner-cone emission.