  A theory of thermal and nonthermal radiation in a vacuum background of
arbitrary temperature generated by relativistic polarizable particle with spin
is proposed. When the particle rotates, radiation is produced by vacuum
fluctuations even in the case of zero temperature of the system. In the
ultrarelativistic case, the spectral-angular intensity of radiation is
concentrated along the velocity of the particle. At finite temperatures of
particle and vacuum, the particle temperature (in its rest frame) rather
quickly acquires an equilibrium magnitude depending on the velocities of
rotation and uniform motion and the background temperature. This equilibrium
temperature determines the intensity of radiation. The dynamical slowing down
takes a very long time until the kinetic energy of uniform motion and rotation
is converted into radiation.
