TY - JOUR
T1 - The role of resonant plasma instabilities in the evolution of blazar-induced pair beams
AU - Perry, Roy
AU - Lyubarsky, Yury
N1 - Funding Information:
This research was supported by the grant 2067/19 from the Israeli Science Foundation.
Publisher Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society
PY - 2021/2/5
Y1 - 2021/2/5
N2 - The fate of relativistic pair beams produced in the intergalactic medium by very high energy emission from blazars remains controversial in the literature. The possible role of resonance beam plasma instability has been studied both analytically and numerically but no consensus has been reached. In this paper, we thoroughly analyse the development of this type of instability. This analysis takes 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 merely in an angular spreading of the beam, which reduces the instability growth rate. For parallel waves, the growth rate is a few times larger than for oblique ones, so they grow faster than oblique waves and drain 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 ∆θ ∼ 10−6 to 10−5. In this case, the width of the resonance for parallel waves, ∝∆θ2, is too small for them to grow in realistic conditions. We perform both analytical estimates and numerical simulations in the quasi-linear regime. These show that for extragalactic beams, the growth of the waves is incapable of taking a significant portion of the beam's energy. This type of instability could at best lead to an expansion of the beam by some factor but the beam's energy remains nearly intact.
AB - The fate of relativistic pair beams produced in the intergalactic medium by very high energy emission from blazars remains controversial in the literature. The possible role of resonance beam plasma instability has been studied both analytically and numerically but no consensus has been reached. In this paper, we thoroughly analyse the development of this type of instability. This analysis takes 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 merely in an angular spreading of the beam, which reduces the instability growth rate. For parallel waves, the growth rate is a few times larger than for oblique ones, so they grow faster than oblique waves and drain 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 ∆θ ∼ 10−6 to 10−5. In this case, the width of the resonance for parallel waves, ∝∆θ2, is too small for them to grow in realistic conditions. We perform both analytical estimates and numerical simulations in the quasi-linear regime. These show that for extragalactic beams, the growth of the waves is incapable of taking a significant portion of the beam's energy. This type of instability could at best lead to an expansion of the beam by some factor but the beam's energy remains nearly intact.
KW - Galaxies: jets
KW - Instabilities
KW - Intergalactic medium
KW - Plasmas
UR - http://www.scopus.com/inward/record.url?scp=85108283495&partnerID=8YFLogxK
U2 - 10.1093/mnras/stab324
DO - 10.1093/mnras/stab324
M3 - Article
SN - 0035-8711
VL - 503
SP - 2215
EP - 2228
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -