Electron and proton heating in trans-relativistic magnetic reconnection

Abstract

Hot collisionless accretion flows, such as the one in Sgr A${}^{\ast }$ at our Galactic center, provide a unique setting for the investigation of magnetic reconnection. Here, protons are non-relativistic while electrons can be ultra-relativistic. By means of two-dimensional particle-in-cell simulations, we investigate electron and proton heating in the outflows of trans-relativistic reconnection (i.e., ${\sigma }_w\sim 0.1-1$, where the magnetization ${\sigma }_w$ is the ratio of magnetic energy density to enthalpy density). For both electrons and protons, we find that heating at high ${\beta }_{\mathrm{i}}$ (here, ${\beta }_{\mathrm{i}}$ is the ratio of proton thermal pressure to magnetic pressure) is dominated by adiabatic compression ('adiabatic heating'), while at low ${\beta }_{\mathrm{i}}$ it is accompanied by a genuine increase in entropy ('irreversible heating'). For our fiducial ${\sigma }_w=0.1$, the irreversible heating efficiency at ${\beta }_{\mathrm{i}}\lesssim 1$ is nearly independent of the electron-to-proton temperature ratio $T_{\mathrm{e}}/T_{\mathrm{i}}$ (which we vary from $0.1$ up to $1$), and it asymptotes to $\sim 2\%$ of the inflowing magnetic energy in the low-${\beta }_{\mathrm{i}}$ limit. Protons are heated more efficiently than electrons at low and moderate ${\beta }_{\mathrm{i}}$ (by a factor of $\sim 7$), whereas the electron and proton heating efficiencies become comparable at ${\beta }_{\mathrm{i}}\sim 2$ if $T_{\mathrm{e}}/T_{\mathrm{i}}=1$, when both species start already relativistically hot. We find comparable heating efficiencies between the two species also in the limit of relativistic reconnection (${\sigma }_w\gtrsim 1$). Our results have important implications for the two-temperature nature of collisionless accretion flows, and may provide the sub-grid physics needed in general relativistic MHD simulations.

29 pages, 27 figures, 7 appendices; accepted to ApJ

References in corpus (10)

• Event-horizon-scale structure in the supermassive black hole candidate at the Galactic Centre
• Advection-Dominated Accretion and the Black Hole Event Horizon
• Relativistic Jets Shine through Shocks or Magnetic Reconnection?
• The Mechanisms of Electron Heating and Acceleration during Magnetic Reconnection
• The Disc-Jet Symbiosis Emerges: Modeling the Emission of Sagittarius A* with Electron Thermodynamics
• Electron Heating During Magnetic Reconnection: A Simulation Scaling Study
• Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-Driven Instabilities and the Electron Heating Mechanism
• Relativistic magnetic reconnection in collisionless ion-electron plasmas explored with particle-in-cell simulations
• Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. II. Electron Heating Efficiency as a Function of Flow Conditions
• Two-Stage Bulk Electron Heating in the Diffusion Region of Anti-Parallel Symmetric Reconnection

Cited by in corpus (21)

• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring
• Observing the Inner Shadow of a Black Hole: A Direct View of the Event Horizon
• The Size, Shape, and Scattering of Sagittarius A* at 86 GHz: First VLBI with ALMA
• Ab Initio Horizon-Scale Simulations of Magnetically Arrested Accretion in Sagittarius A* Fed by Stellar Winds
• Evaluation of New Submillimeter VLBI Sites for the Event Horizon Telescope
• Hybrid-Kinetic Simulations of Ion Heating in Alfvénic Turbulence
• Comparison of the ion-to-electron temperature ratio prescription: GRMHD simulations with electron thermodynamics
• Electron and Proton Heating in Transrelativistic Guide Field Reconnection
• Comptonization by Reconnection Plasmoids in Black Hole Coronae I: Magnetically Dominated Pair Plasma
• GRMHD Simulations and Modeling for Jet Formation and Acceleration Region in AGNs
• Pair Drizzle around Sub-Eddington Supermassive Black Holes
• Radiative Properties of Magnetically-Arrested Disks
• Radiation GRMHD simulations of M87: funnel properties and prospects for gap acceleration
• Combining timing characteristics with physical broadband spectral modelling of black hole X-ray binary GX~339$-$4
• Multi-wavelength Variability of Sagittarius A* in July 2019
• Efficiency of Nonthermal Particle Acceleration in Magnetic Reconnection
• Herschel SPIRE discovery of far-infrared excess synchrotron emission from the west hot spot of the radio galaxy Pictor A
• Scale-invariance of black hole accretion: modeling emission from a black hole X-ray binary with relativistic accretion flow simulations
• Yet Another Modification of Relativistic Magnetohydrodynamic Waves: Electron Thermal Inertia
• PATOKA: Simulating Electromagnetic Observables of Black Hole Accretion
• Non-ideal fields solve the injection problem in relativistic reconnection