Intense 6.7-keV iron line emission from the Galactic Centre


THE Galactic Centre, although obscured by dust at optical wavelengths, is luminous in higher-energy radiation. Gamma-ray observations suggest that a large number of supernovae or novae, or a single supermassive object, has exploded in the Galactic Centre1. Such an explosion will heat up the interstellar medium, probably creating an optically thin hot plasma. Here we report the discovery of intense iron-line emission at 6.7 keV from the Galactic Centre, detected by the Ginga satellite, with characteristics consistent with its production by a shock-heated plasma. The line intensity peaks at the Galactic Centre with a surface brightness of 1.5 x 10−7 erg s−1 sr−1cm−2 and extends over an angular size of 1.8°. The total luminosity of the iron line at the centre region is 2.1 x 1036erg s−1 assuming that the distance to the centre is 10 kpc. The line intensity at the centre is about ten times larger than that from the region of the galactic ridge. The line feature observed is consistent with thermal emission from a thin hot plasma at a temperature of 10 keV. The abundance of iron is estimated to be comparable to or larger than the cosmic abundance. This thin hot plasma is attributable to a shock-heated interstellar medium by an energetic explosion.

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Koyama, K., Awaki, H., Kunieda, H. et al. Intense 6.7-keV iron line emission from the Galactic Centre. Nature 339, 603–605 (1989).

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