Interstellar Absorption of the Low Energy X-rays from the Crab Nebula

Abstract
Observations of the soft X-ray emission from the Crab Nebula, made with the MSSL X-ray telescopes on board the satellite Copernicus, require a review of the currently accepted interstellar abundances of light elements. The soft X-ray data imply a gas column density of (3.1±0.5) × 1021 atoms cm−2 using Brown & Gould X-ray absorption cross-sections. Results obtained from 21 cm radio measurements indicate a lower value of the column density. Better agreement between the X-ray and radio values can be obtained by increasing the abundances of helium and neon over those assumed by Brown & Gould.

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