TOWARD AN EMPIRICAL-THEORY OF PULSAR EMISSION .4. 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 (St), triple (T), and five-component (M) 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, Wcore = 2°.45P-1/2/sin α , established through the study of two-pole interpulsars, indicates that the core-component widths depend only upon the pulsar period P and α, the angle between the rotation and magnetic axes of the star. The relationship can then be used to estimate α in any pulsar with a core component. Values of α are estimated for about 110 core single (St), triple (T), and five-component (M) pulsars. The histogram of α values for core-single pulsars ranges from about 15° to 90° and peaks sharply at about 35°. A similar histogram for triple and five-component stars also peaks at about 35°, but it is broader with α values ranging down to 3°. These stars also exhibit a second peak at 90°. 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.