ChandraObservations of the X‐Ray Halo around the Crab Nebula

Two Chandra observations have been used to search for thermal X-ray emissionfrom within and around the Crab Nebula. Dead-time was minimized by excludingthe brightest part of the Nebula from the field of view. A dust-scattered halocomprising 5% of the strength of the Crab is clearly detected with surfacebrightness measured out to a radial distance of 18 arcminutes. Coverage is 100%at 4 arcminutes, 50% at 12 arcminutes, and 25% at 18 arcminutes. The observedhalo is compared with predictions based on 3 different interstellar grainmodels and one can be adjusted to fit the observation. This dust halo andmirror scattering form a high background region which has been searched foremission from shock-heated material in an outer shell. We find no evidence forsuch emission. We can set upper limits a factor of 10-1000 less than thesurface brightness observed from outer shells around similar remnants. Theupper limit for X-ray luminosity of an outer shell is about 10e34 erg/s.Although it is possible to reconcile our observation with an 8-13 solar massprogenitor, we argue that this is unlikely.Comment: 26 pages, 12 figures, accepted by Ap