The response of black hole spark gaps to external changes: A production mechanism of rapid TeV flares?

TL;DR

This study uses 1D general relativistic particle-in-cell simulations to show how abrupt changes in disk emission and magnetospheric current can trigger delayed, intense TeV flares in black hole magnetospheres, potentially explaining observed rapid flares.

Contribution

It demonstrates that external variations in disk emission and magnetospheric current can induce strong TeV flares via pair production and curvature emission, a novel mechanism for black hole jet variability.

Findings

External changes can cause delayed TeV flares in black hole magnetospheres.

Flare rise time and delay are about the light crossing time of the gap.

The mechanism may explain rapid TeV flares observed in M87 and other AGNs.

Abstract

We study the response of a starved Kerr black hole magnetosphere to abrupt changes in the intensity of disk emission and in the global magnetospheric current, by means of 1D general relativistic particle-in-cell simulations. Such changes likely arise from the intermittency of the accretion process. We find that in cases where the pair production opacity contributed by the soft disk photons is modest, as in, e.g., M87, such changes can give rise to delayed, strong TeV flares, dominated by curvature emission of particles accelerated in the gap. The flare rise time, and the delay between the external variation and the onset of the flare emitted from the outer gap boundary, are of the order of the light crossing time of the gap. The rapid, large amplitude TeV flares observed in M87 and, perhaps, other AGNs may be produced by such a mechanism.