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Non-thermal particle acceleration in collisionless relativistic electron–proton reconnection

TitleNon-thermal particle acceleration in collisionless relativistic electron–proton reconnection
Publication TypeJournal Article
Year of Publication2017
AuthorsWerner, GR, Uzdensky, DA, Begelman, MC, Cerutti, B, Nalewajko, K
JournalMonthly Notices of the Royal Astronomical Society
Volume473
Issue4
Pagination4840 - 4861
Date Published2017-09
ISSN0035-8711
Abstract

Magnetic reconnection in relativistic collisionless plasmas can accelerate particles and power high-energy emission in various astrophysical systems. Whereas most previous studies focused on relativistic reconnection in pair plasmas, less attention has been paid to electron–ion plasma reconnection, expected in black hole accretion flows and relativistic jets. We report a comprehensive particle-in-cell numerical investigation of reconnection in an electron–ion plasma, spanning a wide range of ambient ion magnetizations σi, from the semirelativistic regime (ultrarelativistic electrons but non-relativistic ions, 10−3 ≪ σi ≪ 1) to the fully relativistic regime (both species are ultrarelativistic, σi ≫ 1). We investigate how the reconnection rate, electron and ion plasma flows, electric and magnetic field structures, electron/ion energy partitioning, and non-thermal particle acceleration depend on σi. Our key findings are: (1) the reconnection rate is about 0.1 of the Alfvénic rate across all regimes; (2) electrons can form concentrated moderately relativistic outflows even in the semirelativistic, small-σi regime; (3) while the released magnetic energy is partitioned equally between electrons and ions in the ultrarelativistic limit, the electron energy fraction declines gradually with decreased σi and asymptotes to about 0.25 in the semirelativistic regime; and (4) reconnection leads to efficient non-thermal electron acceleration with a σi-dependent power-law index, p(σi)≃const+0.7σi−1/2.These findings are important for understanding black hole systems and lend support to semirelativistic reconnection models for powering non-thermal emission in blazar jets, offering a natural explanation for the spectral indices observed in these systems.

URLhttps://academic.oup.com/mnras/article/473/4/4840/4265350
DOI10.1093/mnras/stx2530