Pulsar Jets: Implications for Neutron Star Kicks and Initial Spins

By D. Lai, D. Chernoff, Jim Cordes. 2000

213 citations recorded by the source corpus.

We study implications for the apparent alignment of the spin axes, proper motion directions, and polarization vectors of the Crab and Vela pulsars. The spin axes are deduced from recent Chandra X-Ray Observatory images that reveal jets and nebular structure having definite symmetry axes. The alignments indicate that these pulsars were born either in isolation or with negligible velocity contributions from binary motions. We examine the effects of rotation and the conditions under which spin-kick alignment is produced for theoretical models of neutron star kicks. If the kick is generated promptly during the formation of the neutron star by asymmetric mass ejection and/or neutrino emission, then the alignment requires that the proto-neutron star possess, by virtue of the precollapse stellar core's spin, an original spin with period Ps much less than the kick timescale τkick, thus spin averaging the kick forces on the star. The kick timescale ranges from 100 ms to 10 s depending on whether the kick is hydrodynamically driven or neutrino-magnetic field driven. For hydrodynamical models, spin-kick alignment further requires the rotation period of an asymmetry pattern at the radius near shock breakout (≳100 km) to be much less than τkick ≲ 100 ms; this is difficult to satisfy unless rotation plays a dynamically important role in the core collapse and explosion (corresponding to Ps ≲ 1 ms). Aligned kick and spin vectors are inherent to the slow process of asymmetric electromagnetic radiation from an off-centered magnetic dipole. We reassess the viability of this electromagnetic rocket effect, correcting a factor of 4 error in Harrison and Tademaru's calculation that increases the size of the effect. To produce a kick velocity of order a few hundred kilometers per second requires that the neutron star be born with Ps ~ 1 ms and that spin-down due to r-mode-driven gravitational radiation be inefficient compared to standard magnetic braking. The electromagnetic rocket operates on a timescale of order 0.3(B/1013 G)-2 yr. The apparent spin-kick alignment in the Crab and Vela pulsars places important new constraints on each of the mechanisms of neutron star kicks that we consider.

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Citations in the corpus

Supernova simulations from a 3D progenitor model - Impact of perturbations and evolution of explosion properties (2017, background): “The possibility that late-time accretion may explain the spin-kick alignment posited by several observational papers (Lai et al. 2001; Ng & Romani 2007; Noutsos et al. 2013; Rankin 2015) is still more speculative, but remains noteworthy since many alternative mechanisms (see Janka 2017 for an…”
The Spin Periods and Rotational Profiles of Neutron Stars at Birth (2005, background): “These ‘‘pulsar kicks’’ may be a strong indication of the multidimensional nature of the supernovamechanism (Burrows&Hayes 1996; Lai et al. 2001; Fryer 2004; Scheck et al. 2004).”
Asymmetric Supernovae from Magnetocentrifugal Jets (2001, background): “Neutrino asymmetries may yield a short-lived, essentially impulsive effect (Shimizu, Yamada, & Sato 1994; Burrows & Hayes 1996; Fryer & Heger 2000; Lai et al. 2001).”
A statistical study of 233 pulsar proper motions (2005, background): “According to Lai et al. (2001): (1) local convective instabilities in the collapsed stellar core can account for velocities up to ∼100 km s−1; (2) global asymmetric perturbations can create velocities over 1000 km s−1; (3) asymmetric neutrino emission can provide kick velocities up to ∼1000 km s−1;…”
Neutron Star Kicks by the Gravitational Tug-boat Mechanism in Asymmetric Supernova Explosions: Progenitor and Explosion Dependence (2016, background): “…of the kick direction and the spin (rotation) axis of many NSs (e.g. Rankin 2015; Noutsos et al. 2013; Kaplan et al. 2008; Ng & Romani 2007; Lai et al. 2001), but see Bray & Eldridge (2016), who find no statistical evidence of a preferred kick orientation comparing NS velocity…”
Getting Its Kicks: A VLBA Parallax for the Hyperfast Pulsar B1508+55 (2005, background): “Natal kicks from asymmetric SN explosions are believed to be ubiquitous (e.g., Fryer & Kalogera 1997; Portegies Zwart & van den Heuvel 1999; Lai et al. 2001), but the driving mechanism remains unclear.”
Multidimensional supernova simulations with approximative neutrino transport. I. Neutron star kicks and the anisotropy of neutrino-driven explosions in two spatial dimensions (2006, background): “…1996; Goldreich et al. 1996; Lai & Goldreich 2000), strong magnetic fields (Wheeler et al. 2002; Kotake et al. 2004), anisotropic neutrino emission associated with exotic neutrino properties (e.g. Fryer & Kusenko 2006; Fuller et al. 2003), or jets (Cen 1998; Khokhlov et al. 1999; Lai et al. 2001).”
Arecibo Pulsar Survey Using ALFA. I. Survey Strategy and First Discoveries (2005, background): “Additionally, pulsars with especially large space velocities, as revealed through subsequent astrometry, will help constrainaspects of the formation of neutron stars in core-collapse suprnovae (e.g., Lai et al. 2001).”
Three-dimensional neutrino-driven supernovae: neutron star kicks, spins, and asymmetric ejection of nucleosynthesis products (2012, methodology): “Numerous models for producing the kicks have been proposed, either attempting to explain the NS recoil by anisotropic neutrino emission during the Kelvin-Helmholtz cooling of the nascent remnant or by asymmetric mass ejection in the SN explosion (cf. Lai et al. 2001, for a review).”
Three-dimensional simulations of neutrino-driven core-collapse supernovae from low-mass single and binary star progenitors (2018, background): “Although various hypotheses have been formulated to explain this putative finding (see Spruit & Phinney 1998; Lai et al. 2001; Wang et al. 2007 and especially Janka 2017 for a more exhaustive summary of ideas), hydrodynamical simulations have not borne out these ideas so far.”