The First Evidence for Three-dimensional Spin-velocity Alignment in Pulsars

Yao, Jumei

More than 50 years after the discovery of pulsars and confirmation of their association with supernova explosions, the origin of the initial spin and velocity of pulsars remains largely a mystery. The typical space velocities of several hundred km s^−1 have been attributed to “kicks” resulting from asymmetries either in the supernova ejecta or in the neutrino emission. Observations have shown a strong tendency for alignment of the pulsar space velocity and spin axis in young pulsars but, up to now, these comparisons have been restricted to two dimensions. We report here the first evidence for three-dimensional alignment between the spin and velocity vectors, largely based on observations made with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) toward the pulsar PSR J0538+2817 and its associated supernova remnant (SNR) S147. Analyses of the pulsar interstellar scintillation, the pulse polarization of PSR J0538+2817, and proper motion measurements were used to determine the location of the pulsar within the SNR and hence its radial velocity. Current supernova simulations have difficulty producing such 3D alignment. Our results, which depend on the unprecedented instantaneous sensitivity of FAST, add another dimension to the intriguing correlation between pulsar spin-axis and birth-kick directions, thus deepening the mysteries surrounding the birth of neutron stars.