On the Hadronuclear Origin of the TeV Emission of Ap Librae

We investigate the origin of the very-high-energy (VHE; >100 GeV) γ-ray emission from the low-synchrotronpeaked BL Lac object Ap Librae within the framework of a one-zone hadronuclear (PP) interaction model. Conventional leptonic and hadronic scenarios (including photohadronic processes and proton synchrotron emission) have encountered difficulties in reproducing the unusually broad GeV–TeV spectrum of this source without invoking extreme physical conditions. In this work, we construct a one-zone PP model that incorporates both leptonic and hadronuclear components and apply it to fit the multiwavelength spectral energy distribution of Ap Librae. Our results show that the optical-GeV emission can be well explained by leptonic emission from primary electrons, while the TeV emission is naturally accounted for by γ-rays from neutral pion decay in PP interactions. The required total jet power is found to be ∼1.8 × 10⁴⁶ erg·s^-1, which corresponds to half of the Eddington luminosity of the central supermassive black hole. Compared with previous hadronic models that demand superEddington energetics, our approach provides a more physically reasonable explanation for the VHE spectrum of Ap Librae.