Plasma kinetic effects in relativistic radiation-mediated shocks.

Fast shocks that form in optically thick media are mediated by Compton scattering and, if relativistic, pair creation. Since the radiation force acts primarily on electrons and positrons, the question arises of how the force is mediated to the ions which are the dominant carriers of the shock energy. It has been widely thought that a small charge separation induced by the radiation force generates an electric field inside the shock that decelerates the ions. In this paper we argue that, while this is true in subrelativistic shocks which are devoid of positrons, in relativistic radiation mediated shocks (RRMS), which are dominated by newly created e^{+}e^{-} pairs, additional coupling is needed, owing to the opposite electric force acting on electrons and positrons. Specifically, we show that dissipation of the ions energy must involve collective plasma interactions. By constructing a multifluid model for RRMS that incorporates friction forces, we estimate that momentum transfer between electrons and positrons (and/or ions) via collective interactions on scales of tens to thousands of proton skin depths, depending on whether friction is effective only between e^{+}e^{-} pairs or also between pairs and ions, is sufficient to couple all particles and radiation inside the shock into a single fluid. This leaves open the question of whether in relativistic RMS particles can effectively accelerate to high energies by scattering off plasma turbulence. Such acceleration might have important consequences for relativistic shock breakout signals.

Relativistic photon mediated shocks.

A system of equations governing the structure of a steady, relativistic radiation-dominated shock is derived, starting from the general form of the transfer equation obeyed by the photon distribution function. Closure is obtained by truncating the system of moment equations at some order. The anisotropy of the photon distribution function inside the shock is shown to increase with increasing shock velocity, approaching nearly perfect beaming at upstream Lorentz factors Gamma(-) >>1. Solutions of the shock equations are presented for some range of upstream conditions. These solutions are shown to converge as the truncation order is increased.

Detecting energy emissions from a rotating black hole.

The rotational energy of a black hole surrounded by a torus is released through several channels. We have determined that a minor fraction of the energy is released in baryon-poor outflows from a differentially rotating open magnetic flux tube, and a major fraction of about eta/2 is released in gravitational radiation by the torus with angular velocity eta similar 0.2 to 0.5 relative to that of the black hole. We associate the energy emitted in baryon-poor outflows with gamma-ray bursts. The remaining fraction is released in torus winds, thermal emissions, and (conceivably) megaelectron-volt neutrino emissions. The emitted gravitational radiation can be detected by gravitational wave experiments and provides a method for identifying Kerr black holes in the Universe.