Plasma effects on relativistic pair beams from TeV blazars: PIC simulations and analytical predictions

TL;DR

This study investigates how plasma instabilities affect relativistic pair beams from TeV blazars, using analytical models and 2D PIC simulations to understand their impact on gamma-ray signals.

Contribution

The paper introduces an analytical model for realistic pair beam parameters and confirms through simulations that plasma instabilities cause minimal energy loss, highlighting other processes' roles.

Findings

Pair beams experience small changes due to plasma instabilities.

Other processes like magnetic deflection are likely responsible for energy reduction.

Analytical and simulation results align in the studied parameter regime.

Abstract

Pair beams produced by very high-energy radiation from TeV blazars emit gamma rays in the GeV band by inverse-Compton scattering of soft photons. The observed GeV-band signal is smaller than that expected from the full electromagnetic cascade. This means that the pair beams must be affected by other physical processes reducing their energy flux. One possible loss mechanism involves beam-plasma instabilities that we consider in the present work. For realistic parameters the pair beams can not be simulated by modern computers. Instead, we use a simple analytical model to find a range of the beam parameters that (i) provides a physical picture similar to that of realistic pair beams and (ii) at the same time can be handled by available computational resources. Afterwards, we performed corresponding 2D PIC simulations. We confirm that the beams experience only small changes in the relevant parameter regime, and other processes such as deflection in magnetic field must be at play.