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The Universe Viewed in Gamma-Rays 1 The Crab Nebula : 3-dimensional Modeling

We construct an axisymmetric model for the Crab Nebula. The flow dyamics is based on the model by Kennel and Coroniti (1984), but we assume that the kinetic-energy-dominant wind is confined in the equatorial region. We calculate the evolution of the distribution function of the electron-positron plasma flowing out after the shock. Given viewing angles, we reconstruct an image of the nebula and also spatially resolved spectra, and we compare them with the Chandra results. We obtain spacially resolved spectra which agree well with the Chandra results. However, it is found that the assumption of toroidal field does not account for the Chandra image. We need to assume disordered magnetic field with amplitude as large as the mean toroidal field. In addition, brightness contrast between fore and back sides of the ring cannot be reproduced if we assumes that the σ-parameter is as small as ∼ 10−3. We speculate that if the magnetic energy is released by some process making turbulent field in the nebula flow, e.g. by magnetic reconnection, then the difficulties may be resolved: the image can be a ring, and the birightness contrast is higher. The estimate of σ can be larger than previously expected.