X-ray Structure of the Cygnus Loop

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Science  23 Apr 1971:
Vol. 172, Issue 3981, pp. 369-372
DOI: 10.1126/science.172.3981.369


X-ray emission from the Cygnus Loop was observed in the energy region around 0.2 to 1 kiloelectronvolt with a collector that focused x-rays along one dimension while scanning across the nebula. The total integrated intensity is 1.3x 10-8 erg per square centimeter per second. The one-dimensional x-ray structure has the same angular size—about 3 degrees—as the outermost boundaries of the optical filaments. There is no increase in x-ray emission at the center of the nebula nor at the strong feature that is seen in certain radio maps. The x-ray spectrum is consistent with thermal radiation from a hot plasma at a temperature of about 4 x 106 °K with evidence for a line at 19 angstroms corresponding to the 2p→1s transition of O VIII.