SETI at X-ray Energies - Parasitic Searches from Astrophysical Observations

Was published in 1997, but uploaded to arXiv too make it more accessible.

"If a sufficiently advanced civilization can either modulate the emission from an X-ray binary, or make use of the natural high luminosity to power an artificial transmitter, these can serve as good beacons for interstellar communication without involving excessive energy costs to the broadcasting civilization. "

http://arxiv.org/abs/1609.00330

Havn't heard anything lately on this, so maybe never got funded? But i still have postulated that the universal communication standard should be spectral lines, not binary bits.