Generalized, Energy-conserving Numerical Simulations of Particles in General Relativity. II. Test Particles in Electromagnetic Fields and GRMHD

Bacchini, Fabio; Ripperda, Bart; Porth, Oliver; Sironi, Lorenzo

doi:10.3847/1538-4365/aafcb3

Cited by 42 publications

(34 citation statements)

References 78 publications

(123 reference statements)

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“…In future work we plan to address whether plasmoid-structures can form in full 3D simulations and if they can result in orbiting hot spots. In 3D simulations we plan to trace test particles to model radiative signatures with realistic electron distribution functions (Ripperda et al 2018;Ripperda et al 2019a;Bacchini et al 2018Bacchini et al , 2019. The radiative properties of Sgr A * have been studied in ideal GRMHD simulations by Davelaar et al (2018), concluding that 5-10% of the electrons inside the jet's sheath are expected to be accelerated to non-thermal distributions during a flare.…”

Section: Discussionmentioning

confidence: 99%

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Ripperda

Bacchini

Philippov

2020

ApJ

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181

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Hot spots, or plasmoids, forming due to magnetic reconnection in current sheets, are conjectured to power frequent X-ray and near-infrared flares from Sgr A * , the black hole in the center of our Galaxy. It is unclear how, where, and when current sheets form in black-hole accretion disks. We perform axisymmetric general-relativistic resistive magnetohydrodynamics simulations to model reconnection and plasmoid formation in a range of accretion flows. Current sheets and plasmoids are ubiquitous features which form regardless of the initial magnetic field in the disk, the magnetization in the quasisteady-state phase of accretion, and the spin of the black hole. Within 10 Schwarzschild radii from the event horizon, we observe plasmoids forming, after which they can merge, grow to macroscopic scales of the order of a few Schwarzschild radii, and are ultimately advected along the jet's sheath or into the disk. Large plasmoids are energized to relativistic temperatures via reconnection and contribute to the jet's limb-brightening. We find that only hot spots forming in magnetically arrested disks can potentially explain the energetics of Sgr A * flares. The flare period is determined by the reconnection rate, which we find to be between 0.01c and 0.03c in all cases, consistent with studies of reconnection in isolated Harris-type current sheets. We quantify magnetic dissipation and non-ideal electric fields which can efficiently inject non-thermal particles. We show that explicit resistivity allows for converged numerical solutions, such that the electromagnetic energy evolution and dissipation become independent of the grid scale for the extreme resolutions considered here.

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Section: Discussionmentioning

confidence: 99%

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Ripperda

Bacchini

Philippov

2020

ApJ

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181

147

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“…More details on the various •  B preserving schemes and their implementation in BHAC can be found in Olivares et al (2018Olivares et al ( , 2019. Originally designed to study BH accretion in ideal MHD, BHAC has been extended to incorporate nuclear equations of state, neutrino leakage, charged and purely geodetic test particles (Bacchini et al 2018(Bacchini et al , 2019, and nonblack-hole fully numerical metrics. In addition, a nonideal resistive GRMHD module has been developed (e.g., Ripperda et al 2019aRipperda et al , 2019b).…”

Section: Bhacmentioning

confidence: 99%

The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project

Porth

Chatterjee

Narayan

et al. 2019

ApJS

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266

235

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Recent developments in compact object astrophysics, especially the discovery of merging neutron stars by LIGO, the imaging of the black hole in M87 by the Event Horizon Telescope, and high-precision astrometry of the Galactic Center at close to the event horizon scale by the GRAVITY experiment motivate the development of numerical source models that solve the equations of general relativistic magnetohydrodynamics (GRMHD). Here we compare GRMHD solutions for the evolution of a magnetized accretion flow where turbulence is promoted by the magnetorotational instability from a set of nine GRMHD codes: Athena++, BHAC, Cosmos++, ECHO, H-AMR, iharm3D, HARM-Noble, IllinoisGRMHD, and KORAL. Agreement among the codes improves as resolution increases, as measured by a consistently applied, specially developed set of code performance metrics. We conclude that the community of GRMHD codes is mature, capable, and consistent on these test problems.

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“…The particle's equations of motion are deduced from Eq. (6) and Hamilton's equations (Hughes et al 1994;Dodin & Fisch 2010;Bacchini et al 2018Bacchini et al , 2019Parfrey et al 2019):…”

Section: Metricmentioning

confidence: 99%

Synthetic gamma-ray light curves of Kerr black hole magnetospheric activity from particle-in-cell simulations

Crinquand

Cerutti

Dubus

et al. 2021

A&A

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Context. The origin of ultra-rapid flares of very high-energy radiation from active galactic nuclei remains elusive. Magnetospheric processes, occurring in the close vicinity of the central black hole, could account for these flares. Aims. Our aim is to bridge the gap between simulations and observations by synthesizing gamma-ray light curves in order to characterize the activity of a black hole magnetosphere, using kinetic simulations. Methods. We performed global axisymmetric 2D general-relativistic particle-in-cell simulations of a Kerr black hole magnetosphere. We included a self-consistent treatment of radiative processes and plasma supply, as well as a realistic magnetic configuration, with a large-scale equatorial current sheet. We coupled our particle-in-cell code with a ray-tracing algorithm in order to produce synthetic light curves. Results. These simulations show a highly dynamic magnetosphere, as well as very efficient dissipation of the magnetic energy. An external supply of magnetic flux is found to maintain the magnetosphere in a dynamic state, otherwise the magnetosphere settles in a quasi-steady Wald-like configuration. The dissipated energy is mostly converted to gamma-ray photons. The light curves at low viewing angle (face-on) mainly trace the spark gap activity and exhibit high variability. On the other hand, no significant variability is found at high viewing angle (edge-on), where the main contribution comes from the reconnecting current sheet. Conclusions. We observe that black hole magnetospheres with a current sheet are characterized by a very high radiative efficiency. The typical amplitude of the flares in our simulations is lower than is detected in active galactic nuclei. These flares could result from the variation in parameters external to the black hole.

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Generalized, Energy-conserving Numerical Simulations of Particles in General Relativity. II. Test Particles in Electromagnetic Fields and GRMHD

Cited by 42 publications

References 78 publications

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

Magnetic Reconnection and Hot Spot Formation in Black Hole Accretion Disks

The Event Horizon General Relativistic Magnetohydrodynamic Code Comparison Project

Synthetic gamma-ray light curves of Kerr black hole magnetospheric activity from particle-in-cell simulations

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