Abstract
THERE is a serious discrepancy between determinations of the column density of interstellar matter in the direction of the Crab Nebula. Virtually every soft X-ray observation1–5 with sufficient energy resolution to derive this column density yields a result substantially in excess of determinations based on 21-cm absorption6–8. The quality of the X-ray and radio data is now such that this disagreement must represent a genuine physical effect rather than an artefact of the data analysis.
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MARGON, B. Molecular hydrogen in X-ray astronomy. Nature 249, 24–25 (1974). https://doi.org/10.1038/249024a0
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DOI: https://doi.org/10.1038/249024a0
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