High Power Laser Science and Engineering, (2019), Vol. 7, e17, 8 pages.
© The Author(s) 2019. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/
licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
doi:10.1017/hpl.2019.3
Maser radiation from collisionless shocks: application
to astrophysical jets
D. C. Speirs
1
, K. Ronald
1
, A. D. R. Phelps
1
, M. E. Koepke
2
, R. A. Cairns
3
, A. Rigby
4
, F. Cruz
5
,
R. M. G. M. Trines
6
, R. Bamford
6
, B. J. Kellett
6
, B. Albertazzi
7
, J. E. Cross
8
, F. Fraschetti
9
, P. Graham
10
,
P. M. Kozlowski
8
, Y. Kuramitsu
11
, F. Miniati
8
, T. Morita
12
, M. Oliver
8
, B. Reville
13
, Y. Sakawa
12
,
S. Sarkar
8
, C. Spindloe
6
, M. Koenig
7
, L. O. Silva
5
, D. Q. Lamb
14
, P. Tzeferacos
8,14
, S. Lebedev
15
,
G. Gregori
8,14
, and R. Bingham
1,6
1
Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, UK
2
Department of Physics, West Virginia University, Morgantown, WV 26506-6315, USA
3
School of Mathematics and Statistics, University of St. Andrews, Fife, KY16 9SS, UK
4
Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK
5
GoLP/Instituto de Plasmas e Fus
˜
au Nuclear, Instituto Superior T
´
ecnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
6
STFC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, UK
7
Laboratoire pour l’Utilisation de Lasers Intenses, UMR7605, CNRS CEA, Universit
´
e Paris VI Ecole Polytechnique, 91128 Palaiseau
Cedex, France
8
Department of Physics, University of Oxford, Parks Road, Oxford, OX1 3PU, UK
9
Departments of Planetary Sciences and Astronomy, University of Arizona, Tucson, AZ 85721, USA
10
AWE, Aldermaston, Reading, West Berkshire, RG7 4PR, UK
11
Department of Physics, National Central University, Taoyuan 320, China
12
Institute of Laser Engineering, Osaka University, 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan
13
School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK
14
Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637, USA
15
Imperial College London, London, SW72AZ, UK
(Received 30 August 2018; revised 9 January 2019; accepted 21 January 2019)
Abstract
This paper describes a model of electron energization and cyclotron-maser emission applicable to astrophysical
magnetized collisionless shocks. It is motivated by the work of Begelman, Ergun and Rees [Astrophys. J. 625, 51
(2005)] who argued that the cyclotron-maser instability occurs in localized magnetized collisionless shocks such as those
expected in blazar jets. We report on recent research carried out to investigate electron acceleration at collisionless shocks
and maser radiation associated with the accelerated electrons. We describe how electrons accelerated by lower-hybrid
waves at collisionless shocks generate cyclotron-maser radiation when the accelerated electrons move into regions of
stronger magnetic fields. The electrons are accelerated along the magnetic field and magnetically compressed leading to
the formation of an electron velocity distribution having a horseshoe shape due to conservation of the electron magnetic
moment. Under certain conditions the horseshoe electron velocity distribution function is unstable to the cyclotron-maser
instability [Bingham and Cairns, Phys. Plasmas 7, 3089 (2000); Melrose, Rev. Mod. Plasma Phys. 1, 5 (2017)].
Keywords: laboratory astrophysics; plasma physics; particle acceleration; plasma-wave instabilities
Correspondence to: D. C. Speirs, Department of Physics, University
of Strathclyde, John Anderson Building, Glasgow, G4 0NG, UK. Email:
david.c.speirs@strath.ac.uk
1