Production of metagalactic X-rays by relativistic dust grains

The relativistic dust grains which may be responsible for ultra-high energy cosmic rays, as suggested by the present author, interact with the cosmic black-body radiation. This results in the energy loss of the relativistic dust grains, so that their energy spectrum is cut-off at the Lorentz factor as large as 2×10³ (0.1/a), wherea is the grain radius. The black-body radiation is scattered and absorbed by the dust grains. The photons scattered and reemitted contribute to metagalactic X-rays. The X-ray intensity estimated is comparable to the observed one in the soft X-ray region.