Photon breeding - a new particle acceleration mechanism - and the high-energy emission from relativistic jets
High-energy photons propagating in the magnetised medium with large velocity gradients can mediate energy and momentum exchange. Conversion of these photons into electron-positron pairs in the field of soft photons with the consequent isotropization and emission of new high-energy photons by Compton scattering can lead to the avalanche of the high-energy photons and pairs fed by the bulk energy of the flow. This is the essence of the photon breeding mechanism.
We study the problem of high-energy emission of relativistic jets in blazars via photon breeding mechanism using 2D ballistic model for the jet with the detailed treatment of particle propagation and interactions. Our numerical simulations from the first principles demonstrate that a jet propagating in the soft radiation field of broad-emission line region can convert a significant fraction of its total power into radiation. The photon breeding mechanism produces a population of high-energy electrons (and positrons) and, therefore, alleviate the need for alternative (Fermi-type) particle acceleration mechanisms that have not yet been shown to produce high-energy leptons self-consistently. The mechanism reproduces basic spectral features observed in blazars including the blazar sequence (shift of spectral peaks towards lower energies at higher luminosities). The significant deceleration of the jet at sub parsec scales reconciles the discrepancy between the high Doppler factors determined by the fits to the spectra of TeV blazars and low apparent velocities observed at VLBI scales. The mechanism produces significantly broader angular distribution of radiation than that predicted by simple model assuming an isotropic emission in the jet frame. This helps to reconcile the observed statistics of FR I and BL Lac objects with the large Lorentz factors of the jets.