New light on the X-ray spectrum of the Crab Nebula

XMM-Newton observations of the Crab provide new information on its integrated X-ray spectrum and the variation of the spectral form across the nebula. The Crab pulsar and its surrounding torus exhibit the hardest spectra with power-law indices of $\Gamma = 1.6$ and 1.8. The jet and outer reaches of the nebula are significantly softer with $\Gamma = 2.1$ and 2.3 respectively. For the whole nebula, the huge number of recorded counts allows a detailed examination of the soft X-ray absorption due to cool gas in the foreground of the Crab. Absorption edges due to oxygen and neon are clearly identified. Oxygen and iron in the interstellar medium are underabundant by a factor of $0.63 \pm 0.01$. The average $N_{\rm H}=3.45\pm0.02 10^{21}$ cm-2 and varies by less than $\pm11\%$ on a scale equal to or larger than 20 arcsec over the face of the nebula. These observations of the Crab provide an excellent demonstration of the power of the EPIC cameras on XMM-Newton for spatial, spectral and timing studies.

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