Exploring the impact of electromagnetic dissipation on ultra-relativistic plasma outflows
Argyrios Loules, Nektarios Vlahakis
TL;DR
The paper investigates how electromagnetic dissipation shaping ultra-relativistic plasma outflows, such as those associated with gamma-ray bursts, alters jet acceleration and collimation. It develops a self-similar, axisymmetric resistive relativistic MHD framework in Schwarzschild geometry and produces exact near-axis jet solutions that include resistive effects via Ohm's law and a variable adiabatic index EOS. By comparing an ideal MHD solution with two resistive cases (R1, R2) that activate resistivity at different radii, the study reveals that EM dissipation can both suppress thermal acceleration and heat the flow, thereby changing the Lorentz factor and enhancing collimation through thermal and magnetic mechanisms. A key finding is a dissipation profile that scales as $\theta^2$, along with toroidal field amplification and an electric potential gradient along poloidal field lines driven by increased field-line rotation $\Omega$, underpinning the dissipation and its impact on jet dynamics.
Abstract
Ultra-relativistic plasma outflows are intrinsically connected with gamma-ray bursts. Over the years, a large number of analytical and numerical works has been devoted to understanding the intricacies of their complex dynamics, with most of these past studies performed in the ideal MHD regime. We propose a self-similar formalism, based on the expansion of the equations of resistive relativistic magnetohydrodynamics, for the description of these outflows in the vicinity of their symmetry axis and present semi-analytical solutions describing strongly relativistic jets in both the ideal and resistive MHD regimes. Our solutions provide a clear picture of the impact of electromagnetic dissipation on the acceleration and collimation mechanisms which determine the kinetic and morphological characteristics of these relativistic outflows. The resistive MHD solutions are compared to their ideal MHD counterparts, revealing the key differences between the two regimes. Our comparative analysis sheds light on the possible role of electromagnetic dissipation in shaping the dynamics of the ultra-relativistic outflows associated with gamma-ray bursts.