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Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
The detection of rapidly variable gamma-ray emission in active galactic
nuclei has generated renewed interest in magnetospheric particle acceleration
and emission scenarios. In order to explore its potential, we study the
possibility of steady gap acceleration around the null surface of a rotating
black hole magnetosphere. We employ a simplified (1D) description along with
the general relativistic expression of Gauss's law, and we assume that the gap
is embedded in the radiation field of a radiatively inefficient accretion flow.
The model is used to derive expressions for the radial distribution of the
parallel electric field component, the electron and positron charge density,
the particle Lorentz factor, and the number density of $\gamma$-ray photons. We
integrate the set of equations numerically, imposing suitable boundary
conditions. The results show that the existence of a steady gap solution for a
relative high value of the global current is in principle possible if charge
injection of both species is allowed at the boundaries. We present gap
solutions for different choices of the global current and the accretion rate.
When put in context, our results suggest that the variable very high energy
$\gamma$-ray emission in M87 could be compatible with a magnetospheric origin.
