Radiation from relativistic jets in blazars and the efficient dissipation of their bulk energy via photon breeding

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Abstract
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 runaway cascade of the high-energy photons and electron-positron 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. The gamma-ray background of similar energy density as observed at Earth is sufficient to trigger the photon breeding. As a result, a jet can convert up to 80 per cent of its total power into radiation. Photon breeding produces a population of high-energy pairs and predicts the spectra in agreement with observations of blazars (e.g. the blazar sequence). It also decelerates the jet at subparsec scales and induces the transversal gradient of the Lorentz factor which reconcile the discrepancy between the high Doppler factors determined from the spectra of TeV blazars and the low apparent velocities observed at VLBI scales. The broad angular distribution of radiation predicted by the mechanism reconciles the observed statistics and luminosity ratio of FR I and BL Lac objects with the large Lorentz factors of the jets as well as explains the high level of the TeV emission in the radio galaxy M87. (abridged)

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