The jets of the Vela pulsar

Abstract

Chandra observations of the Vela pulsar-wind nebula (PWN) have revealed a jet in the direction of the pulsar’s proper motion, and a counter-jet 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 thirteen Chandra observations spread over ≈2.5 years 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 time-scales of days to weeks. 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 3×10 30 erg s −1, compared to 6×10 32 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, ∼2×10 14 eV, and energy injection rate, ∼8×10 33 erg s −1, for the outer jet. In the summed PWN image we see a dim, ∼2′-long outer counter-jet, which also shows a power-law spectrum with Γ≈1.2–1.5. Southwest of the jet/counter-jet (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.