2017ApJ...835..164O

Based on the collective linear and nonlinear processes in a magnetized plasma surrounding the black hole at the Galactic center (GC), an acceleration mechanism is proposed to explain the recent detection/discovery of PeV protons. In a two-stage process, the gravitation energy is first converted to the electrical energy in fast-growing Langmuir waves, and then the electrical energy is transformed to the particle kinetic energy through Landau damping of waves. It is shown that, for the characteristic parameters of GC plasma, proton energy can be boosted up to 5 PeV.