Vela Pulsar and Its Synchrotron Nebula

By D. Helfand, E. Gotthelf, J. Halpern. 2000

245 citations recorded by the source corpus.

We present high-resolution Chandra X-ray observations of PSR B0833-45, the 89 ms pulsar associated with the Vela supernova remnant. We have acquired two observations separated by 1 month to search for changes in the pulsar and its environment following an extreme glitch in its rotation frequency. We find a well-resolved nebula with a toroidal morphology remarkably similar to that observed in the Crab Nebula, along with an axial Crab-like jet. Between the two observations, taken ~3 × 105 s and ~3 × 106 s after the glitch, the flux from the pulsar is found to be steady to within 0.75%; the 3 σ limit on the fractional increase in the pulsar's X-ray flux is ≲10-5 of the inferred glitch energy. We use this limit to constrain parameters of glitch models and neutron star structure. We do find a significant increase in the flux of the nebula's outer arc; if associated with the glitch, the inferred propagation velocity is ≳0.7c, similar to that seen in the brightening of the Crab Nebula wisps. We propose an explanation for the X-ray structure of the Vela synchrotron nebula based on a model originally developed for the Crab Nebula. In this model, the bright X-ray arcs are the shocked termination of a relativistic equatorial pulsar wind that is contained within the surrounding kidney-bean shaped synchrotron nebula comprising the postshock, but still relativistic, flow. In a departure from the Crab model, the magnetization parameter σ of the Vela pulsar wind is allowed to be of order unity; this is consistent with the simplest MHD transport of magnetic field from the pulsar to the nebula, where B ≤ 4 × 10-4 G. The inclination angle of the axis of the equatorial torus with respect to the line of sight is identical to that of the rotation axis of the pulsar as previously measured from the polarization of the radio pulse. The projection of the rotation axis on the sky may also be close to the direction of proper motion of the pulsar if previous radio measurements were confused by orthogonal-mode polarized components. We review effects that may enhance the probability of alignment between the spin axis and space velocity of a pulsar, and speculate that short-period, slowly moving pulsars are just the ones best-suited to producing synchrotron nebulae with such aligned structures. Previous interpretations of the compact Vela nebula as a bow-shock in a very weakly magnetized wind suffered from data of inadequate spatial resolution and less plausible physical assumptions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/429a4c56a2d9090487aee75f1c14f3c921d83509

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Citations in the corpus

Evidence for alignment of the rotation and velocity vectors in pulsars. II. Further data and emission heights (2005, methodology): “In order to compare this with the polarization position angle, Helfand et al. (2001) used the results of Hamilton et al. (1977) who measured the polarization PA at the peak of the total intensity and obtained an angle of 64◦ (or 244◦).”
Axially symmetric relativistic MHD simulations of Pulsar Wind Nebulae in Supernova Remnants. On the origin of torus and jet-like features (2004, unknown): “Similar features have been observed also in a number of other objects, namely around the Vela pulsar (Helfand et al. 2001; Pavlov et al. 2003), PSR 1509-58 (Gaensler et al. 2002) and in the supernova remnants G0.”
The Variable Jet of the Vela Pulsar (2003, background): “The latter values are smaller than the ¼ 155 , inferred by Helfand et al. (2001) under the assumption that the PWN arcs are Dopler-brightened parts of a torus around the jet/counterjet, and they are smaller then the ¼ 152 suggested by Pavlov (2000),3 assuming the arcs are Doppler-brightened parts…”
Asymmetric Supernovae from Magnetocentrifugal Jets (2001, background): “Some imbalance in axial jets can also account for pulsar runaway velocities, specifically velocities that are parallel to the spin axis (Helfand et al. 2001 and references therein).”
Fitting Pulsar Wind Tori (2003, methodology): “We model this with identical tori, symmetrically offset along the torus axis about the pulsar by distance d, following Helfand et al. (2001).”
Magnetars in the Metagalaxy: An Origin for Ultra-High-Energy Cosmic Rays in the Nearby Universe (2002, background): “4 (Gaensler et al. 2002), and perhaps in the Vela nebula (Helfand et al. 2001), where the energy in the pulsar wind gets transferred to the plasma forming the observed synchrotron nebulae, suggests that an interestingly large fraction of the total voltage does get applied to a Goldreich-Julian flux…”
The Vela Pulsar’s Proper Motion and Parallax Derived from VLBI Observations (2003, methodology): “The extra accuracy we can provide refines the conclusion reached by Pavlov et al. (2000); Helfand et al. (2001) for the Vela alignment.”
DIRECT OBSERVATION OF THE COOLING OF THE CASSIOPEIA A NEUTRON STAR (2010, background): “…from external causes, e.g., accretion of circumstellar gas or asteroids (e.g. Jura 2003; Cordes & Shannon 2008), or from internal sources, e.g., by the same mechanism that is responsible for pulsar glitches (van Riper et al. 1991; Seward et al. 2000; Helfand et al. 2001, and references therein).”
Synchrotron nebulae created by anisotropic magnetized pulsar winds (2004, methodology): “7 shows the simulated X-ray maps for the ξ = 0.5 model at different epochs for the same angle between the line of sight and the polar axis as derived for the Crab and the Vela nebulae, 60◦ (Weisskopf et al. 2000; Helfand et al. 2001).”
The Magnetorotational Instability in Core-Collapse Supernova Explosions (2002, background): “The fact that pulsars like those in the Crab and Vela remnants have jetlike protrusions (Weisskopf et al. 2000; Helfand et al. 2001) also encourages this line of thought.”