Toward an empirical theory of pulsar emission. IV - Geometry of the core emission region

The core-component widths of pulsars with interpulses are studied in an effort to define the geometric properties of the core emission region. The results are then applied to a large population of core-single, triple, and five-component pulsars which all have core components. Core-component widths are intimately related to the polar-cap geometry at the stellar surface. A simple mathematical expression, established through the study of two-pole interpulsars, indicates that the core-component widths depend only upon the pulsar period and alpha, the angle between the rotation and magnetic axes of the star. The relationship can then be used to estimate alpha in any pulsar with a core component. Values of alpha are estimated for about 110 core single (St), triple (T), and five-component (M) pulsars. These results have important implications for the nature of the core radiation process. Core emission appears to come essentially from the stellar surface, filling the entire polar-cap 'gap' region where particle acceleration is thought to take place.