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Title:
Spatial Variation of the X-Ray Spectrum of the Crab Nebula
Authors:
Mori, Koji; Burrows, David N.; Hester, J. Jeff; Pavlov, George G.; Shibata, Shinpei; Tsunemi, Hiroshi
Affiliation:
AA(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802; ), AB(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802; ), AC(Department of Physics and Astronomy, Box 871504, Arizona State University, Tyler Mall, Tempa, AZ 85287-1504), AD(Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802), AE(Department of Physics, Yamagata University, Yamagata 990-8560, Japan), AF(Department of Earth and Space Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan)
Publication:
The Astrophysical Journal, Volume 609, Issue 1, pp. 186-193. (ApJ Homepage)
Publication Date:
07/2004
Origin:
UCP
ApJ Keywords:
ISM: Individual: Name: Crab Nebula, ISM: Supernova Remnants, X-Rays: ISM
DOI:
10.1086/421011
Bibliographic Code:
2004ApJ...609..186M

Abstract

We present a spectral analysis of the Crab Nebula obtained with the Chandra X-ray observatory. The X-ray spectrum is characterized by a power law whose index varies across the nebula. The variation can be discussed in terms of the particle injection from the pulsar in two different directions: the equatorial plane containing the torus and the symmetry axis along the jet. In the equatorial plane, spectra within the torus are the hardest, with a photon index α~1.9, and are almost independent of the surface brightness. At the periphery of the torus, the spectrum gradually softens in the outer, lower surface brightness regions, up to α~3.0. This indicates that synchrotron losses become significant to X-ray-emitting particles at the outer boundary of the torus. We discuss the nature of the torus, incorporating information from observations at other wavelengths. Spectral variations are also seen within the southern jet. The core of the jet is the hardest, with α~2.0, and the outer sheath surrounding the core becomes softer with α up to 2.5 at the outermost part. Based on the similarity between the spectra of the jet core and the torus, we suggest that the electron spectra of the particles injected from the pulsar are also similar in these two different directions. The brightness ratio between the near and far sides of the torus can be explained by Doppler boosting and relativistic aberration; however, the observed ratio cannot be derived from the standard weakly magnetized pulsar wind model. We also found a site where an optical filament comprising supernova ejecta is absorbing the soft X-ray emission (<2 keV).
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