Emission beam geometry of selected pulsars derived from average pulse polarization data

By fitting the classical rotating vector model (RVM) to high-quality polari zation data for selected radio pulsars, we find the inclination of the magn etic axis to the spin axis, alpha, as well as the minimum angle between the line of sight and the magnetic axis, beta, for 10 objects. We give a full treatment of statistical errors in the fitting process. We also present a d ictionary and conversion table of various investigators' geometric definiti ons to facilitate future comparisons. We compare our results with other RVM fits and with empirical/geometrical (E/G) approaches, and we examine the s trengths and weaknesses of RVM fits and E/G investigations for the determin ation of pulsar emission beam geometry. Our fits to B0950+08 show that it i s an orthogonal rotator with the main and interpulse radiation emitted from opposite magnetic poles, whereas earlier RVM fits indicated that it is an almost-aligned, single-magnetic pole emitter. We demonstrate that low-level emission across a wide longitude range, when properly weighted in the RVM fit, conclusively favors the former scenario. B0823+26 is also an orthogona l rotator. We find that B1929+10 emits into its wide observed range of long itudes from portions of a single cone that is almost aligned with the spin axis. This result agrees with other RVM fits but conflicts with the E/G fin dings of Rankin & Rathnasree. We determine that convergent RVM solutions ca n be found only for a minority of pulsars: generally those having emission over a relatively wide longitude range, and especially those pulsars having interpulse emission. In pulsar B0823+26, our preferred fit to data at all longitudes yields a solution differing by several sigma from a fit to the m ain pulse/postcursor combination alone. For pulsar B0950+08, separate fits to the main pulse region, the interpulse region, and our preferred fit to a lmost all longitudes, converge to results differing by several times the fo rmal uncertainties. These results indicate that RVM fits are easily perturb ed by systematic effects in polarized position angles and that the formal u ncertainties significantly underestimate the actual errors.