FRB Coherent Emission from Decay of Alfven Waves. (arXiv:2004.00644v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kumar_P/0/1/0/all/0/1">Pawan Kumar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bosnjak_Z/0/1/0/all/0/1">Z. Bosnjak</a>
We present a model for FRBs where a large amplitude Alfven wave packet is
launched by a disturbance near the surface of a magnetar, and a substantial
fraction of the wave energy is converted to coherent radio waves at a distance
of a few tens of neutron star radii. The wave amplitude at the magnetar surface
should be about 1011G in order to produce a FRB of isotropic luminosity
10$^{44}$ erg s$^{-1}$. An electric current along the static magnetic field is
required by Alfven waves with nonzero component of transverse wave-vector. The
current is supplied by counter-streaming electron-positron pairs, which have to
move at nearly the speed of light at larger radii as the plasma density
decreases with distance from the magnetar surface. The counter-streaming pairs
are subject to two-stream instability which leads to the formation of particle
bunches of size of order $c/omega_p$; where $omega_p$ is plasma frequency. A
strong electric field develops along the static magnetic field when the wave
packet arrives at a radius where electron-positron density is insufficient to
supply the current required by the wave. The electric field accelerates
particle bunches along the curved magnetic field lines, and that produces the
coherent FRB radiation. We provide a number of predictions of this model.
We present a model for FRBs where a large amplitude Alfven wave packet is
launched by a disturbance near the surface of a magnetar, and a substantial
fraction of the wave energy is converted to coherent radio waves at a distance
of a few tens of neutron star radii. The wave amplitude at the magnetar surface
should be about 1011G in order to produce a FRB of isotropic luminosity
10$^{44}$ erg s$^{-1}$. An electric current along the static magnetic field is
required by Alfven waves with nonzero component of transverse wave-vector. The
current is supplied by counter-streaming electron-positron pairs, which have to
move at nearly the speed of light at larger radii as the plasma density
decreases with distance from the magnetar surface. The counter-streaming pairs
are subject to two-stream instability which leads to the formation of particle
bunches of size of order $c/omega_p$; where $omega_p$ is plasma frequency. A
strong electric field develops along the static magnetic field when the wave
packet arrives at a radius where electron-positron density is insufficient to
supply the current required by the wave. The electric field accelerates
particle bunches along the curved magnetic field lines, and that produces the
coherent FRB radiation. We provide a number of predictions of this model.
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