A Relativistic Electron-Positron Outflow from a Tepid Fireball

TL;DR

This paper uses numerical simulations to show that relativistic electron-positron outflows can be generated by radiative acceleration from nearly pair-equilibrium states, with most pairs surviving despite low initial temperatures.

Contribution

It demonstrates the formation of relativistic outflows from tepid fireballs through radiative acceleration, challenging previous assumptions about pair annihilation during expansion.

Findings

Relativistic outflows with Lorentz factor ~7 can be produced.

Most pairs survive during the outflow despite low temperatures.

Dynamical timescales are short enough to prevent significant annihilation.

Abstract

Through detailed numerical simulations, we demonstrate that relativistic outflows (Lorentz factor $\Gamma \sim 7$) of electron-positron pairs can be produced by radiative acceleration even when the flow starts from a nearly pair equilibrium state at subrelativistic temperatures. Contrary to the expectation that pairs annihilate during an expansion stage for such low temperatures, we find that most pairs can survive for the situations obtained in our previous work. This is because in the outflow-generating region the dynamical timescale is short enough even though the fireball is optically thick to scattering. Several problems that should be solved to apply to actual active galactic nucleus jets are discussed.