Abstract
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 one-dimensional 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 teraelectronvolt (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 active galactic nuclei may be produced by such a mechanism.
Highlights
Many active galactic nuclei (AGNs) occasionally exhibit rapidly variable TeV emission, the origin of which is yet unknown
Particle acceleration by the gap electric field gives rise to copious pair creation through the interaction of particles accelerated in the gap with soft photons emitted by the accretion flow
We studied the response of a black hole spark gap to external changes by means of 1D general relativistic Particle-in-Cell (GRPIC) simulations
Summary
Many active galactic nuclei (AGNs) occasionally exhibit rapidly variable TeV emission, the origin of which is yet unknown. It has been proposed that charge starved magnetospheric regions (spark gaps) might provide sites for variable TeV emission (Levinson 2000; Levinson & Rieger 2011; Hirotani et al 2016, 2017; Levinson & Segev 2017). The amplitude of the variations and the overall luminosity were found to depend rather sensitively on the pair creation opacity contributed by the soft radiation emitted from the surrounding accretion flow. These simulations invoke steady external conditions, the soft photon intensity that is given as input. We find that the gap response is highly non-linear by virtue of Klein-Nishina (KN) effects and the sensitive dependence of the curvature radiation power on the energy of emitting particles, and that such changes can lead to production of strong flares of curvature TeV emission by the gap accelerating particles
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