Faint X-ray Structure in the Crab Pulsar-wind Nebula

We report on a Chandra observation of the Crab Nebula that gives the first clear view of the faint boundary of the Crab's X-ray-emitting Pulsar Wind Neb-ula, or PWN. There is structure in all directions. Fingers, loops, bays, and the South Pulsar Jet all indicate that either filamentary material or the magnetic field are controlling the relativistic electrons. In general, spectra soften as distance from the pulsar increases but do not change rapidly along linear features. This is particularly true for the Pulsar Jet. The termination of the Jet is abrupt; the E side is close to an [O III] optical filament which may be blocking propagation on this side. We argue that linear features have ordered magnetic fields and that the structure is determined by the synchrotron lifetime of particles diffusing perpendicular and parallel to the magnetic field. We find no significant evidence for thermal X-rays inside the filamentary envelope. The Crab Nebula was one of the first extrasolar sources known to emit X-rays. It was detected with a rocket-borne detector on 1962 October 12 (Gursky et al. 1963), recognized in data from a flight on 1963 April 29 (Bowyer et al. 1964a) and observed again during a 1964 July 7 lunar occultation. The occultation showed the X-ray source to have an extent of ∼ 1 ′ and to be located at the center of the 5 ′ × 7 ′ optical nebula (Bowyer et al. 1964b). The morphology of the source has since been measured with increasingly better resolution by a second lunar occultation (Palmieri et al.