1998A&A...338..971B

The small dispersion in the observed relation between period and intrinsic opening angles of the conal emission regions in pulsars can be used to study their geometry. Applying this direct method shows the corresponding hollow cones to be consistent with being circular; an upper limit of approximately 10% is derived for the deviation from a circular geometry. Previous investigations have relied on assumptions regarding the statistical properties of the pulsar sample used in the analysis. The disparate conclusions reached in the past concerning the geometry of pulsar beams is traced to the sensitivity of such indirect methods to the validity of these assumptions. It is further argued that there is no observational evidence for an evolution with pulsar age of the angle between the cone axis and rotation axis.