Effective Resistivity in Relativistic Collisionless Reconnection

• Published in: The Astrophysical journal Vol. 950; no. 2; pp. 169 - 177
• Main Authors: Selvi, S., Porth, O., Ripperda, B., Bacchini, F., Sironi, L., Keppens, R.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01-06-2023; IOP Publishing
• Subjects: Astronomy & Astrophysics; Astrophysics; Compact objects; Electric fields; Electrical resistivity; High energy astrophysics; Magnetic fields; Magnetic reconnection; Magnetohydrodynamics; Ohm's Law; Plasma astrophysics; Relativistic effects; Relativity; Statistical analysis; Tensors
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/acd0b0

Abstract
Magnetic reconnection can power spectacular high-energy astrophysical phenomena by producing nonthermal energy distributions in highly magnetized regions around compact objects. By means of two-dimensional fully kinetic particle-in-cell (PIC) simulations, we investigate relativistic collisionless plasmoid-mediated reconnection in magnetically dominated pair plasmas with and without a guide field. In X-points, where diverging flows result in a nondiagonal thermal pressure tensor, a finite residence time for particles gives rise to a localized collisionless effective resistivity. Here, for the first time for relativistic reconnection in a fully developed plasmoid chain, we identify the mechanisms driving the nonideal electric field using a full Ohm law by means of a statistical analysis based on our PIC simulations. We show that the nonideal electric field is predominantly driven by gradients of nongyrotropic thermal pressures. We propose a kinetic physics motivated nonuniform effective resistivity model that is negligible on global scales and becomes significant only locally in X-points. It captures the properties of collisionless reconnection with the aim of mimicking its essentials in nonideal magnetohydrodynamic descriptions. This effective resistivity model provides a viable opportunity to design physically grounded global models for reconnection-powered high-energy emission.