The Variable Jet of the Vela Pulsar

By G. Pavlov, M. Teter, O. Kargaltsev, D. Sanwal. 2003

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Observations of the Vela pulsar-wind nebula (PWN) with the Chandra X-Ray Observatory have revealed a complex, variable PWN structure, including inner and outer arcs, a jet in the direction of the pulsar's proper motion, and a counterjet in the opposite direction, embedded in diffuse nebular emission. The jet consists of a bright, 8'' long inner jet, between the pulsar and the outer arc, and a dim, curved outer jet that extends up to ~100'' in approximately the same direction. From the analysis of 13 Chandra observations spread over ≈2.5 yr we found that this outer jet shows particularly strong variability, changing its shape and brightness. We observed bright blobs in the outer jet moving away from the pulsar with apparent speeds (0.3-0.6)c and fading on timescales of days to weeks. If the blobs are carried away by a flow along the jet, the observed variations suggest mildly relativistic flow velocities, about (0.3-0.7)c. The spectrum of the outer jet fits a power-law model with a photon index Γ = 1.3 ± 0.1. For a distance of 300 pc, the apparent average luminosity of the outer jet in the 1-8 keV band is about 3 × 1030 ergs s-1, compared to 6 × 1032 from the whole PWN within 42'' from the pulsar. The X-ray emission of the outer jet can be interpreted as synchrotron radiation of ultrarelativistic electrons/positrons. This interpretation allows one to estimate the magnetic field, ~100 μG, maximum energy of X-ray-emitting electrons, ~2 × 1014 eV, and energy injection rate, ~8 × 1033 ergs s-1, for the outer jet. In the summed PWN image, we see a faint, strongly bent, extension of the outer jet. This bending could be caused by combined action of a wind within the supernova remnant, with a velocity of a few ×10 km s-1, along with the ram pressure due to the pulsar's proper motion. The more extreme bends closer to the pulsar, as well as the apparent side motions of the outer jet, can be associated with kink instabilities of a magnetically confined, pinched jet flow. Another feature found in the summed image is a dim, ~2' long outer counterjet, which also shows a power-law spectrum with Γ ≈ 1.2-1.5. Southwest of the jet/counterjet (i.e., approximately perpendicular to the direction of pulsar's proper motion), an extended region of diffuse emission is seen. Relativistic particles responsible for this radiation are apparently supplied by the outer jet.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d90b8688b76fa8b3313451f648c456c0c6168c16

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Citations in the corpus

Fitting Pulsar Wind Tori (2003, background): “Pavlov et al. (2003) report an inner jet spectral index 1:1, which with our best-fit gives j ¼ 0:45, in remarkably good agreement with our torus .”
Synchrotron nebulae created by anisotropic magnetized pulsar winds (2004, methodology): “Indeed, the mere fact that both the jet and the counter-jet are seen in the images of the Crab and the Vela nebulae (Weisskopf et al. 2000; Helfand et al. 2001) alone rules out ultrarelativistic speeds.”
Axially symmetric relativistic MHD simulations of Pulsar Wind Nebulae in Supernova Remnants. On the origin of torus and jet-like features (2004, result): “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.”
Three-dimensional magnetohydrodynamic simulations of the Crab nebula (2013, result): “Recently, Durant et al. (2013) showed that the Vela pulsar jet can be modelled as a helix, steadily turning on the timescale of 400 days.”
The evolution and structure of pulsar wind nebulae (2006, background): “Evidence for the effects of kink instabilities is seen in the curved nature of many PWN jets, particularly for the Vela PWN where the jet morphology is observed to change dramatically on timescales of months (Pavlov et al. 2003).”