A Simple Model for the Observed Pulse Profiles of Precessing Pulsars and its Application to PSR B1913+16

Abstract

The spin axis of some pulsars precesses due to body asymmetries, binary companions, or other effects. The spin precession causes our line of sight to drift slowly across the emission beam, leading to secular changes in the observed pulse profile. Studies of these variations thus provide a unique tool to reveal the two‐dimensional structure of the emission beam.Weisberg & Taylor [1, 2] found that an hourglass‐shaped beam was required in order to successfully model their observations of pulse profile changes in the binary pulsar B1913+16, which undergoes relativistic geodetic spin precession. We define here a novel coordinate system to aid in visualization of the observing geometry. We then present a circular beam model and show that this simple model can exhibit quite complicated pulse profile changes. We revisit the question of whether elaborate beam models are needed to explain the observations of PSR B1913+16. We find that the circular model qualitatively matches the data for B1913+16, but that additional parameters are needed for a good fit.