Resolving the extragalactic hard X-ray background

  title={Resolving the extragalactic hard X-ray background},
  author={Richard F. Mushotzky and Lennox L. Cowie and Amy J. Barger and Keith A. Arnaud},
The origin of the hard (2–10 keV) X-ray background has been a mystery for over 35 years. Most of the soft X-ray background has been resolved into individual sources (mainly quasars), but these sources do not have the spectral energy distribution required to match the spectrum of the X-ray background as a whole. Here we report the results of a deep survey, using the Chandra satellite, in which the detected hard X-ray sources account for at least 75 per cent of the hard X-ray background. The mean… 

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