  We describe the structure and implementation of a radiation hydrodynamic
solver for MANGA, the moving-mesh hydrodynamics module of the large-scale
parallel code, Charm N-body GrAvity solver (ChaNGa). We solve the equations of
time dependent radiative transfer using a reduced speed of light approximation
following the algorithm of Jiang et al (2014). By writing the radiative
transfer equations as a generalized conservation equation, we solve the
transport part of these equations on an unstructured Voronoi mesh. We then
solve the source part of the radiative transfer equations following Jiang et al
(2014) using an implicit solver, and couple this to the hydrodynamic equations.
The use of an implicit solver ensure reliable convergence and preserves the
conservation properties of these equations even in situations where the source
terms are stiff due to the small coupling timescales between radiation and
matter. We present the results of a limited number of test cases (energy
conservation, momentum conservation, dynamic diffusion, linear waves, crossing
beams, and multiple shadows) to show convergence with analytic results and
numerical stability. We also show that it produces qualitatively the correct
results in the presence of multiple sources in the optically thin case.
