  In the absence of a sufficient amount of plasma injection into the black hole
(BH) magnetosphere, the force-free state of the magnetosphere cannot be
maintained, leading to the emergence of strong, time-dependent, longitudinal
electric field (spark gap). Recent studies of supermassive BH magnetospheres by
using analytical methods and particle-in-cell (PIC) simulations propose the
possibility of the efficient particle acceleration and consequent gamma-ray
emissions in the spark gap. In this work, we perform one-dimensional general
relativistic PIC simulations to examine the gamma-ray emission from
stellar-mass BH magnetospheres. We find that intermittent spark gaps emerge and
particles are efficiently accelerated, in a similar manner to the supermassive
BH case. We build a semi-analytic model of the plasma dynamics and radiative
processes which reproduces the maximum electron energies and peak gamma-ray
luminosities in the simulation results. Based on this model, we show that
gamma-ray signals from stellar-mass BHs wandering through the interstellar
medium could be detected by gamma-ray telescopes such as the Fermi Large Area
Telescope, or the Cherenkov Telescope Array.
