Suppression of the TeV pair-beam plasma instability by a tangled weak intergalactic magnetic field

TL;DR

This paper investigates how weak, tangled intergalactic magnetic fields suppress the electrostatic instability of blazar-induced pair beams, impacting secondary gamma-ray emission and offering insights into cosmic magnetic field effects.

Contribution

It demonstrates that weak intergalactic magnetic fields can significantly suppress the beam-plasma instability, reducing the energy loss of pair beams at much lower field strengths than previously thought.

Findings

Weak magnetic fields increase transverse momentum of pair beam particles.

Electrostatic instability is eliminated at fields three orders of magnitude below magnetic deflection threshold.

Intermediate-strength fields pose unresolved questions about gamma-ray observations.

Abstract

We study the effect of a tangled sub-fG level intergalactic magnetic field (IGMF) on the electrostatic instability of a blazar-induced pair beam. Sufficiently strong IGMF may significantly deflect the TeV pair beams, which would reduce the flux of secondary cascade emission below the observational limits. A similar flux reduction may result from the electrostatic beam-plasma instability, which operates the best in the absence of IGMF. Considering IGMF with correlation lengths smaller than a kpc, we find that weak magnetic fields increase the transverse momentum of the pair beam particles, which dramatically reduces the linear growth rate of the electrostatic instability and hence the energy-loss rate of the pair beam. We show that the beam-plasma instability is eliminated as an effective energy-loss agent at a field strength three orders of magnitude below that needed to suppress the secondary cascade emission by magnetic deflection. For intermediate-strength IGMF, we do not know a viable process to explain the observed absence of GeV-scale cascade emission.