Dynamical solutions are always of interest to people in gravity theories. We
derive a series of generalized Vaidya solutions in the n-dimensional de
Rham-Gabadadze-Tolley (dRGT) massive gravity with a singular reference metric.
Similar to the case of the Einstein gravity, the generalized Vaidya solution
can describe shining/absorbing stars. Moreover, we also find a more general
Vaidya-like solution by introducing a more generic matter field than the pure
radiation in the original Vaidya spacetime. As a result, the above generalized
Vaidya solution is naturally included in this Vaidya-like solution as a special
case. We investigate the thermodynamics for this Vaidya-like spacetime by using
the unified first law, and present the generalized Misner-Sharp mass. Our
results show that the generalized Minser-Sharp mass does exist in this
spacetime. In addition, the usual Clausius relation δQ=TdS holds on
the apparent horizon, which implicates that the massive gravity is in a
thermodynamic equilibrium state. We find that the work density vanishes for the
generalized Vaidya solution, while it appears in the more general Vaidya-like
solution. Furthermore, the covariant generalized Minser-Sharp mass in the
n-dimensional de Rham-Gabadadze-Tolley massive gravity is also derived by
taking a general metric ansatz into account.Comment: 10 pages, no figure, version published in PR