Showing papers by "Cherry Ng published in 2007"

Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars

Abstract: Evidence from pulsar wind nebula symmetry axes and radio polarization observations suggests that pulsar motions correlate with the spin directions. We assemble this evidence for young isolated pulsars and show how it can be used to quantitatively constrain birth kick scenarios. We illustrate by computing several plausible, but idealized, models where the momentum thrust is proportional to the neutrino cooling luminosity of the proto-neutron star. Our kick simulations include the effects of pulsar acceleration and spin-up and our maximum likelihood comparison with the data constrains the model parameters. The fit to the pulsar spin and velocity measurements suggests that (1) the anisotropic momentum required amounts to ~10% of the neutrino flux, (2) while a prekick spin of the star is required, the preferred magnitude is small 10-20 rad s-1, so that for the best-fit models (3) the bulk of the spin is kick-induced with ~ 120 rad s-1 and (4) the models suggest that the anisotropy emerges on a timescale τ ~ 1-3 s.

The Origin and Motion of PSR J0538+2817 in S147

Abstract: We report on Very Long Baseline Array (VLBA) astrometry and Chandra imaging of PSR J0538+2817 in the supernova remnant S147. We measure a parallax distance of 1.47 kpc along with a high-precision proper motion, giving a transverse velocity V⊥ = 400 km s-1. A small extended wind nebula is detected around the pulsar; the symmetry axis of this structure suggests that the spin axis lies 12° ± 4° from the velocity vector (two-dimensional), but the emission is too faint for robust model-independent statements. The neutron star is hot, consistent with the young ~40 kyr kinematic age. The pulsar progenitor is likely a runaway from a nearby cluster, with NGC 1960 (M36) a leading candidate.

Fitting Pulsar Wind Tori. II. Error Analysis and Applications

Abstract: We have applied the torus fitting procedure described in Ng & Romani (2004) to PWNe observations in the Chandra data archive. This study provides quantitative measurement of the PWN geometry and we characterize the uncertainties in the fits, with statistical errors coming from the fit uncertainties and systematic errors estimated by varying the assumed fitting model. The symmetry axis $\Psi$ of the PWN are generally well determined, and highly model-independent. We often derive a robust value for the spin inclination $\zeta$. We briefly discuss the utility of these results in comparison with new radio and high energy pulse measurements

Birth Kick Distributions and the Spin-Kick Correlation of Young Pulsars

Abstract: Evidence from pulsar wind nebula symmetry axes and radio polarization observations suggests that pulsar motions correlate with the spin directions. We assemble this evidence for young isolated pulsars and show how it can be used to quantitatively constrain birth kick scenarios. We illustrate by computing several plausible, but idealized, models where the momentum thrust is proportional to the neutrino cooling luminosity of the proto-neutron star. Our kick simulations include the effects of pulsar acceleration and spin-up and our maximum likelihood comparison with the data constrains the model parameters. The fit to the pulsar spin and velocity measurements suggests that: i) the anisotropic momentum required amounts to ~10% of the neutrino flux, ii) while a pre-kick spin of the star is required, the preferred magnitude is small 10-20rad/s, so that for the best-fit models iii) the bulk of the spin is kick-induced with $\bar \Omega$ ~120rad/s and iv) the models suggest that the anisotropy emerges on a timescale $\tau$ ~1-3s.