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P: Fachverband Plasmaphysik

P 17: Astrophysical Plasmas

P 17.2: Talk

Thursday, March 31, 2022, 14:15–14:30, P-H11

Suppression of the TeV pair-beam plasma instability by a weak intergalactic magnetic field — •Mahmoud Alawashra¹ and Martin Pohl^1,2 — ¹Institute for Physics and Astronomy, University of Potsdam, D-14476 Potsdam, Germany — ²Deutsches Elektronen-Synchrotron DESY, Platanenallee 6, 15738 Zeuthen, Germany

We constrain the intermediate-scale intergalactic magnetic field (IGMF) through its suppression of the electrostatic instability for blazar-induced pair beams. IGMF of femto-Gauss strength are sufficient to significantly deflect the TeV pair beams, which reduces 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 at zero IGMF. We study the effect of sub-fG level IGMF on the electrostatic instability of the blazar-induced pair beam. Considering IGMF with correlation lengths smaller than a few kpc, we find that such 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. Our results show that the IGMF eliminates the beam-plasma instability 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.