Can Pulsar Masses be Determined ?

Abstract

THE sudden speed-up^1,2 of the Vela pulsar PSR 0833–45 offers an unusual opportunity to study the interior of a neutron star. In a previous article³, the behaviour of the pulsar after the speed-up was analysed in terms of a simple two-component model. One component is the crust and the charged particles in the interior, which are strongly coupled to each other electromagnetically, and the second is the interior neutron superfluid. The initial spin-up of the star is assumed to take place in the crust (as a consequence of a starquake⁴), and is communicated in a time ∼10² s to the charged particles in the interior. The interior neutron superfluid takes a very much longer time, τ_c ∼ 2 yr, to respond to the increased angular velocity of the crust-charged particle system. In this note we wish to point out that observation of the time dependence of the pulse repetition frequency after the starquake makes possible a determination of the pulsar mass, provided that one knows the type of deformation leading to the speed-up of the pulsar.