A Lepton–Hadron Model for the Multi-Wavelength Emission from Extreme High-Frequency Peaked BL Lacertae 1ES 1218+304

We develop a lepton–hadron model for the possible origin of hard very high energy (VHE) spectra from a distant blazar. The model includes synchrotron self-Compton (SSC) and hadronic components. The lepton components include synchrotron radiation and inverse Compton scattering of relativistic electrons. For the hadronic components, we consider proton synchrotron radiation and investigate the interaction of protons with the synchrotron emission soft photons or cosmic microwave background (CMB) photons. Upon adopting the parametrization of the observed spectrum of 1ES 1218+304, we obtain the following results: (1) the model is able to match the spectral energy distribution of 1ES 1218+304; (2) we find that in Ep≈1010∼1017eV, the π0→γ-ray process contributes the majority of the secondary photons; and (3) the interaction of protons with the low-energy photons may occur in or outside the jet.