The role of plasma instabilities in relativistic radiation mediated shocks

Relativistic radiation mediated shocks (RRMS) dictate the early emission in numerous transient sources such as supernovae, low luminosity gamma-ray bursts, binary neutron star mergers, and tidal disruption events. These shock waves are mediated by Compton scattering and copious electron-positron pair creation. It has been pointed out recently that a high pair multiplicity inside the shock transition leads to a lepton-baryon velocity separation, prone to plasma instabilities [1]. The interaction of the different species with this radiation-mediated microturbulence can lead to coupling and heating that is unaccounted for by current single-fluid models.  

Here, we present a theoretical analysis of the hierarchy of plasma microinstabilities growing in an electron-ion plasma loaded with pairs and subject to a radiation force. Our results are validated by particle-in-cell simulations that probe the nonlinear regime of the instabilities, and the lepton-baryon coupling in the microturbulent electromagnetic field. Based on this analysis, we derive a reduced transport equation for the particles, that demonstrates nonadiabatic compression in a Joule-like heating process by the joined contributions of the decelerating turbulence, radiation force, and electrostatic field. Our results suggest that the radiation-mediated microturbulence could have important consequences for the radiative signatures of RRMS.

[1] Levinson A., 2020, Phys. Rev. E, 102, 063210