On proton synchrotron blazar models: the case of quasar 3C 279

TL;DR

This paper introduces a new method to estimate the minimum Doppler factor and energy content of the gamma-ray emitting region in quasar 3C 279, based on proton synchrotron models and photon quenching principles, impacting our understanding of blazar energetics.

Contribution

It presents an innovative estimation technique for Doppler factors in proton synchrotron blazar models using photon quenching, extending traditional equipartition methods to hadronic scenarios.

Findings

Photon quenching sets an upper limit on gamma-ray luminosity.

Doppler factors above a certain threshold are necessary to explain TeV observations.

Modeling can minimize energy density and jet power with high Doppler factors.

Abstract

In the present work we propose an innovative estimation method for the minimum Doppler factor and energy content of the gamma-ray emitting region of quasar 3C 279, using a standard proton synchrotron blazar model and the principles of automatic photon quenching. The latter becomes relevant for high enough magnetic fields and results in spontaneous annihilation of gamma-rays. The absorbed energy is then redistributed into electron-positron pairs and soft radiation. We show that as quenching sets an upper value for the source rest-frame gamma-ray luminosity, one has, by neccessity, to resort to Doppler factors that lie above a certain value in order to explain the TeV observations. The existence of this lower limit for the Doppler factor has also implications on the energetics of the emitting region. In this aspect, the proposed method can be regarded as an extension of the widely used one for estimating the equipartition magnetic field using radio observations. In our case, the leptonic synchrotron component is replaced by the proton synchrotron emission and the radio by the VHE gamma-ray observations. We show specifically that one can model the TeV observations by using parameter values that minimize both the energy density and the jet power at the cost of high-values of the Doppler factor. On the other hand, the modelling can also be done by using the minimum possible Doppler factor; this, however, leads to a particle dominated region and high jet power for a wide range of magnetic field values. Despite the fact that we have focused on the case of 3C 279, our analysis can be of relevance to all TeV blazars favoring hadronic modelling that have, moreover, simultaneous X-ray observations.