Radiative signatures of electron-ion shocks in blazar jets

Abstract: Shocks are promising sites of particle acceleration in extragalactic jets. In electron-ion shocks, electrons can be heated up to large Lorentz factors, making them an attractive explanation for the high minimum electron Lorentz factors regularly needed to model blazar SEDs. Still, the thermal electron component is commonly neglected when modelling observations. In this talk, we present a multi-wavelength modelling of the blazar Mrk421 employing a particle distribution whose shape is directly motivated by predictions of plasma PIC simulations. We demonstrate that fluxes in the optical/UV and MeV-GeV bands efficiently restrict the emission from the thermal (relativistic) Maxwellian electrons, allowing us to obtain constraints on the shock properties. Notably, we find that at least ~10% of the shock energy must be transferred to the nonthermal electrons in order to stay compatible with the fluxes in the optical/UV and MeV-GeV bands. These results are almost insensitive to the shock velocity, although radio observations suggest a shock Lorentz factor above ~5. In the second part of the talk, we present preliminary results of dedicated PIC simulations to verify under which physical conditions of electron-ion shocks these findings can be matched.