  Langevin equations for the self-thermophoretic dynamics of Janus motors
partially coated with an absorbing layer that is heated by a radiation field
are presented. The derivation of these equations is based on fluctuating
hydrodynamics and radiative heat transfer theory involving stochastic equations
for bulk phases and surface processes that are consistent with microscopic
reversibility. Expressions for the self-thermophoretic force and torque for
arbitrary slip boundary conditions are obtained. The overdamped Langevin
equations for the colloid displacement and radiative heat transfer provide
expressions for the self-thermophoretic velocity and its reciprocal
contribution where an external force can influence the radiative heat transfer.
A nonequilibrium fluctuation formula is also derived and shows how the
probability density of the Janus particle displacement and radiation energy
transfer during the time interval [0,t] are related to the mechanical and
thermal affinities that characterize the nonequilibrium system state.
