Thermal Interpretation of Schwinger Effect in Near-Extremal RN Black Hole

We propose a thermal interpretation of the Schwinger effect for charged scalars and spinors in an extremal and near-extremal Reissner-Nordstr\"{o}m (RN) black hole. The emission of charges has the distribution with an effective temperature determined by the Davies-Unruh temperature for accelerating charges by the electric field and the scalar curvature of AdS_2 from the near-horizon geometry AdS_2 X S^2. We find a charge bound for the extremal micro black hole to remain stable against the Schwinger emission in analogy with the Breitenlohlner-Freedman bound for the AdS space. In the in-out formalism we find the one-loop QED effective action consistent with the vacuum persistence and interpret the vacuum persistence as the leading Schwinger effect and the effect of a charged vacuum of the Coulomb field.