Electron positron pairs in blazar jets and gamma-ray loud radio-galaxies

TL;DR

This paper investigates the role of electron-positron pairs in blazar jets and gamma-ray loud radio galaxies, suggesting pairs can be produced in the inner jet zone and impact jet power estimates, with observable implications.

Contribution

It proposes a model where pair creation occurs in the inner jet zone, affecting jet composition and luminosity estimates, and links observable gamma-ray flux to pair production processes.

Findings

Pairs can outnumber electrons by 10-20 times in jets.

Inner jet zone can produce enough pairs if gamma-ray luminosity exceeds 1e44 erg/s.

Detectable gamma-ray emission from pair production is possible in radio galaxies at certain flux levels.

Abstract

The matter content of extragalactic relativistic jets is still an unsolved issue. There are strong arguments against pure electron-positron pair jets, but pairs could outnumber the electrons associated with protons by a factor 10-20. This impacts on the estimate of the jet kinetic power, by reducing it by the same factor, and on the total energy delivered to leptons by the particle acceleration mechanism. Pairs cannot be created in the same jet-zone responsible for the high energy gamma-ray emission we see in blazars, because the reprocessing of the created pairs would overproduce the X-ray flux. Copious pair creation could occur in the inner zone of the still accelerating jet, where the bulk Lorentz factor is small. It is found that the inner zone can produce a sufficient number of pairs to replenish the zone of the jet where most of the luminosity is emitted, but only if the gamma-ray luminosity of the inner jet is above 1e44 erg/s at ~1 MeV. Since the beaming is modest, this emission can be observed at large viewing angles, and detected in radio-galaxies and lobe dominated quasars at the flux level of 1e-12 - 1e-11 erg/cm2/s for a source at a redshift z=0.1.