Particle-in-cell simulations of pair discharges in a starved magnetosphere of a Kerr black hole

TL;DR

This paper uses advanced simulations to study pair discharges near Kerr black holes, revealing self-sustained cascades, TeV gamma-ray emissions, and potential explanations for observed TeV flares in M87.

Contribution

It introduces a new general relativistic particle-in-cell simulation method to model pair discharges and gamma-ray emissions in black hole magnetospheres, highlighting the role of pair cascades and TeV emissions.

Findings

Gap screening occurs via plasma oscillations and pair cascades.

Gamma-ray spectrum peaks in the TeV band with specific luminosity.

Prompt discharge phase releases stored potential energy as TeV flares.

Abstract

We investigate the dynamics and emission of a starved magnetospheric region (gap) formed in the vicinity of a Kerr black hole horizon, using a new, fully general relativistic particle-in-cell code that implements Monte Carlo methods to compute gamma-ray emission and pair production through the interaction of pairs and gamma rays with soft photons emitted by the accretion flow. It is found that when the Thomson length for collision with disk photons exceeds the gap width, screening of the gap occurs through low-amplitude, rapid plasma oscillations that produce self-sustained pair cascades, with quasi-stationary pair and gamma-ray spectra, and with a pair multiplicity that increases in proportion to the pair production opacity. The gamma-ray spectrum emitted from the gap peaks in the TeV band, with a total luminosity that constitutes a fraction of about $10^{-5}$ of the corresponding Blandford-Znajek power. This stage is preceded by a prompt discharge phase of duration $\sim r_g/c$, during which the potential energy initially stored in the gap is released as a flare of curvature TeV photons. We speculate that the TeV emission observed in M87 may be produced by pair discharges in a spark gap.