Electron-positron beams in intergalactic medium

by Mr. Roy Perry

at Astrophysics and Cosmology Seminar

Wed, 13 May 2020, 11:00
Sacta-Rashi Building for Physics (54), room 207


There is a lot of controversy about the fate of relativistic pair beams produced in the intergalactic medium by ultra-high energy emission from blazars. The possible role of the resonance beam plasma instability has been studied both analytically and numerically, but no consensus has been reached. In this work, we thoroughly analyze the development of the instability taking into account that a highly relativistic beam loses energy only due to interactions with the plasma waves propagating within the opening angle of the beam (we call them parallel waves), whereas excitation of oblique waves results in merely an angular spreading of the beam, which reduces the instability rate. For parallel waves, the growth rate is larger than for oblique ones by a factor of a few, so that generally they indeed grow faster and take the energy from the beam before it expands. However, the specific property of extragalactic beams is that they are extraordinarily narrow; the opening angle is only 1e-6 – 1e-5. In this case, the width of the resonance for parallel waves is so small that they are unable to grow at realistic conditions. We perform both analytical estimates and numerical simulations in the quasilinear regime and show that for extragalactic beams, the growth of the waves capable of taking the energy of the beam is totally suppressed. The instability could at best lead to an expansion of the beam a few times, but the energy of the beam remains nearly intact.

Created on 10-05-2020 by Zitrin, Adi (zitrin)
Updaded on 10-05-2020 by Zitrin, Adi (zitrin)