General Relativistic Geodetic Spin Precession in Binary Pulsar B1913+16: Mapping the Emission Beam in Two Dimensions

We have carefully measured the pulse profile of the binary pulsar PSRB1913+16 at 21 cm wavelength for twenty years, in order to search forvariations that result from general relativistic geodetic precession of thespin axis. The profile width is found to decrease with time in its innerregions, while staying essentially constant on its outer skirts. We fit thesedata to a model of the beam shape and precession geometry. Four equivalentsolutions are found, but evolutionary considerations and polarization dataselect a single preferred model. While the current data sample only a limitedrange of latitudes owing to the long precessional cycle, the preferred modelshows a beam elongated in the latitude direction and hourglass--shaped.Comment: Accepted by AP