Relativistic Magnetic Reconnection in Electron–Positron–Proton Plasmas: Implications for Jets of Active Galactic Nuclei

Journal Article · 23 July 2019 · The Astrophysical Journal (Online)

DOI: https://doi.org/10.3847/1538-4357/ab287a · OSTI ID:1612631

Petropoulou, Maria  ^[1]; Sironi, Lorenzo ^[2]; Spitkovsky, Anatoly ^[1]; Giannios, Dimitrios ^[3]

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1. Princeton Univ., NJ (United States)
2. Columbia Univ., New York, NY (United States)
3. Purdue Univ., West Lafayette, IN (United States); Univ. of Crete, Heraklion (Greece); Foundation for Research and Technology Hellas, Heraklion (Greece)

Magnetic reconnection is often invoked to explain the nonthermal radiation of relativistic outflows, including jets of active galactic nuclei (AGNs). Motivated by the largely unknown plasma composition of AGN jets, we study reconnection in the unexplored regime of electron–positron–proton (pair-proton) plasmas with large-scale two-dimensional particle-in-cell simulations. We cover a wide range of pair multiplicities (lepton-to-proton number ratio κ = 1–199) for different values of the all-species plasma magnetization (σ = 1, 3, and 10) and electron temperature ($${{\rm{\Theta }}}_{e}\equiv {{kT}}_{e}/{m}_{e}{c}^{2}=0.1\mbox{--}100$$). We focus on the dependence of the post-reconnection energy partition and lepton energy spectra on the hot pair plasma magnetization $${\sigma }_{e,h}$$ (i.e., the ratio of magnetic to pair enthalpy densities). We find that the post-reconnection energy is shared roughly equally between magnetic fields, pairs, and protons for $${\sigma }_{e,h}$$ gsim 3. We empirically find that the mean lepton Lorentz factor in the post-reconnection region depends on σ, Θ e , and $${\sigma }_{e,h}$$ as $$\langle {\gamma }_{e}-1\rangle \approx \sqrt{\sigma }(1+4{{\rm{\Theta }}}_{e})\left(1+{\sigma }_{e,h}/30\right)$$, for σ ≥ 1. The high-energy part of the post-reconnection lepton energy distributions can be described by a power law, whose slope is mainly controlled by $${\sigma }_{e,h}$$ for κ gsim 3–6, with harder power laws obtained for higher magnetizations. We finally show that reconnection in pair-proton plasmas with multiplicities κ ~ 1–20, magnetizations σ ~ 1–10, and temperatures Θ e ~ 1–10 results in particle power-law slopes and average electron Lorentz factors that are consistent with those inferred in leptonic models of AGN jet emission.

• Research Organization: Columbia Univ., New York, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC); Lyman Jr. Spitzer Postdoctoral Fellowship; Fermi Guest Investigation; National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); Simons Foundation
• Grant/Contract Number: SC0016542; 80NSSC18K1745; 267233; ATP NNX17AG21G; AST-1816136
• OSTI ID: 1612631
• Journal Information: The Astrophysical Journal (Online), Vol. 880, Issue 1; ISSN 1538-4357
• Publisher: Institute of Physics (IOP)Copyright Statement
• Country of Publication: United States
• Language: English