Proton energy spectra du_p/dlnϵ ≡ ϵ² dn/dϵ vs. proton energy ϵ for three characteristic scenarios described in the text. For each panel, the energy density distribution is shown in units of the background plasma pressure. Top panel: Stochastic acceleration in the turbulent corona, with a characteristic Alfvénic velocity v_A ≃ 0.2 c (see text for details), for model (1) and (2), corresponding to the solid and dashed lines, respectively. Middle panel: Combination of stochastic acceleration in the corona with shear acceleration at the base of the jet (see text for the details of the physical parameters). The stochastic contribution is indicated by dotted lines, the shear contribution by dashed lines, and the sum of the two by solid lines. The different colors correspond to models (1) and (2). For the top and middle panels, the normalization of the energy density in accelerated particles has been fixed in order to reproduce the inferred proton flux. Bottom panel: Modeling of stochastic acceleration, accounting for self-regulation by particle feedback on the turbulence (damping), for a characteristic Alfvén velocity v_A ≃ 0.2 c. The plasma β parameter is 0.5 (see Appendix A).