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We explore the physics of relativistic radiation mediated shocks (RRMSs) inthe regime where photon advection dominates over photon generation. For thispurpose, a novel iterative method for deriving a self-consistent steady-statestructure of RRMS is developed, based on a Monte-Carlo code that solves thetransfer of photons subject to Compton scattering and pairproduction/annihilation. Systematic study is performed by imposing variousupstream conditions which are characterized by the following three parameters:the photon-to-baryon inertia ratio $\xi_{u *}$, the photon-to-baryon numberratio $\tilde{n}$, and the shock Lorentz factor $\gamma_u$. We find that theproperties of RRMSs vary considerably with these parameters. In particular,while a smooth decline in the velocity, accompanied by a gradual temperatureincrease is seen for $\xi_{u*} \gg 1$, an efficient bulk Comptonization, thatleads to a heating precursor, is found for $\xi_{u*} \lesssim 1$. As aconsequence, although particle acceleration is highly inefficient in theseshocks, a broad non-thermal spectrum is produced in the latter case. Thegeneration of high energy photons through bulk Comptonization leads, in certaincases, to a copious production of pairs that provide the dominant opacity forCompton scattering. We also find that for certain upstream conditions a weaksubshock appears within the flow. For a choice of parameters suitable togamma-ray bursts, the radiation spectrum within the shock is found to becompatible with that of the prompt emission, suggesting that subphotosphericshocks may give rise to the observed non-thermal features despite the absenceof accelerated particles.

Monte-Carlo simulations of relativistic radiation mediated shocks: I. photon rich regime