  Active Galactic Nuclei in general, and the supermassive black hole in M87 in
particular, show bright and rapid gamma-ray flares up to energies of 100 GeV
and above. For M87, the flares show multiwavelength components, and the
variability timescale is comparable to the dynamical time of the event horizon,
suggesting that the emission may come from a compact region nearby the nucleus.
However, the emission mechanism for these flares is not well understood. Recent
high-resolution general-relativistic magnetohydrodynamic simulations show the
occurrence of episodic magnetic reconnection events that can power flares
nearby the black hole event horizon. In this work, we analyze the radiative
properties of the reconnecting current layer under the extreme plasma
conditions applicable to the black hole in M87 from the first principles. We
show that abundant pair production is expected in the vicinity of the
reconnection layer, to the extent that the produced secondary pair plasma
dominates the reconnection dynamics. Using analytic estimates backed by
two-dimensional particle-in-cell simulations we demonstrate that in the
presence of strong synchrotron cooling, reconnection can produce a hard
power-law distribution of pair plasma imprinted in the outgoing synchrotron (up
to a few tens of MeV) and the inverse-Compton signal (up to TeV). We produce
synthetic radiation spectra from our simulations, which can be directly
compared with the results of future multiwavelength observations of M87*
flares.
