INTERSTELLAR ABSORPTION OF LOW-ENERGY X-RAYS FROM CRAB-NEBULA

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. © 1973 Royal Astronomical Society.