Cooling timescales of particles accelerated at the base of the jet (left) and at the terminal region (right). We show the energy gains and losses for electrons in the top panel and the same for protons in the bottom panel. In the internal shock at the base of the jet, the particles cool mainly by the synchrotron mechanism due to the strong magnetic field, reaching energies of 10 GeV (electrons) and 50 PeV (protons). At the reverse shock in the terminal region of the jet, electrons also cool mainly by synchrotron radiation, reaching energies of 5 PeV, while protons reach energies of ∼10 PeV. The efficiency of the acceleration in all cases is η_acc ∼ 0.1.