Plasma effects on fast pair beams: Kinetic instability of parallel electrostatic waves
by
Steffen Krakau(Bochum University)
→
Europe/Berlin
Building 67, SemRm 10 (DESY Hamburg)
Building 67, SemRm 10
DESY Hamburg
Description
The interaction of TeV gamma rays from distant blazars with the extragalactic background light (EBL) produces relativistic electron-positron pair beams by the photon-photon annihilation process. The FERMI non-detection of GeV gamma rays, produced by the inverse Compton scattering of these electron-positron pair beams with the EBL, are firstly explained by the existence of an intergalactic magnetic field and the involved deflection of the electron-positron beam. Using the linear instability analysis in the kinetic limit, which properly accounts for the longitudinal and the small but finite perpendicular momentum spread in the pair momentum distribution function, the growth rate of parallel propagating electrostatic oscillations in the intergalactic medium is calculated. We demonstrate, that the created pair beam distribution function is quickly unstable in the unmagnetized intergalactic medium, confirming earlier conclusions by Broderick et al. (2012) and us. Therefore, there is no need to require the existence of small intergalactic magnetic fields. In particular, the various derived lower bounds for the intergalactic magnetic fields are invalid due to the pair beam instability argument.