The role of plasma instabilities in relativistic radiation-mediated shocks: stability analysis and particle-in-cell simulations

• Published in: Monthly notices of the Royal Astronomical Society Vol. 511; no. 2; pp. 3034 - 3045
• Main Authors: Vanthieghem, A, Mahlmann, J F, Levinson, A, Philippov, A, Nakar, E, Fiuza, F
• Format: Journal Article
• Language: English
• Published: United Kingdom Oxford University Press 16.02.2022
• Subjects: analytical; ASTRONOMY AND ASTROPHYSICS; instabilities; methods; numerical; plasmas; radiation mechanisms; shock waves; methods: analytical; plasmas; methods: numerical; instabilities; radiation mechanisms: general; shock waves
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stac162

ABSTRACT Relativistic radiation-mediated shocks are likely formed in prodigious cosmic explosions. The structure and emission of such shocks are regulated by copious production of electron–positron pairs inside the shock-transition layer. It has been pointed out recently that substantial abundance of positrons inside the shock leads to a velocity separation of the different plasma constituents, which is expected to induce a rapid growth of plasma instabilities. In this paper, we study the hierarchy of plasma microinstabilities growing in an electron-ion plasma loaded with pairs and subject to a radiation force. Linear stability analysis indicates that such a system is unstable to the growth of various plasma modes which ultimately become dominated by a current filamentation instability driven by the relative drift between the ions and the pairs. These results are validated by particle-in-cell simulations that further probe the non-linear regime of the instabilities, and the pair-ion coupling in the microturbulent electromagnetic field. Based on this analysis, we derive a reduced-transport equation for the particles via pitch-angle scattering in the microturbulence and demonstrate that it can couple the different species and lead to non-adiabatic compression via a Joule-like heating. The heating of the pairs and, conceivably, the formation of non-thermal distributions, arising from the microturbulence, can affect the observed shock-breakout signal in ways unaccounted for by current single-fluid models.