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

¹ Institute for Physics and Astronomy, University of Potsdam, 14476 Potsdam, Germany
e-mail: rafighi@uni-potsdam.de
² DESY, Platanenallee 6, 15738 Zeuthen, Germany
³ Instytut Fizyki Ja¸drowej PAN, ul. Radzikowskiego 152, 31-342 Kraków, Poland

Received: 8 May 2017
Accepted: 22 August 2017

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 cannot 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 two-dimensional (2D) particle-in-cell (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.