Faraday conversion as a diagnostic of Fast Radio Burst progenitors. (arXiv:1812.07889v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Vedantham_H/0/1/0/all/0/1">H. K. Vedantham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ravi_V/0/1/0/all/0/1">V. Ravi</a>
The extreme, time-variable Faraday rotation observed in the repeating fast
radio burst (FRB) 121102 demonstrates that some FRBs originate in dense and
dynamic magneto-ionic environments. Here we show that besides rotation of the
linear-polarisation vector (Faraday rotation), such media will generally
convert linear to circular polarisation (Faraday conversion). We use the
stringent constraints on circularly polarised emission in bursts from FRB
121102 to conclude the following. (i) All one-zone models where the persistent
radio source associated with FRB 121102 and the Faraday rotation are generated
by the same relativistic plasma are ruled out. (ii) The Faraday rotation must
occur in non-relativistic plasma where the characteristic magnetic field, $B$,
is determined to within a factor of order unity: $10,{rm mG}lesssim B
lesssim 30,{rm mG}$. (iii) The value of $B$ is close to the equipartition
magnetic field of the persistent radio source associated with FRB 121102,
suggesting that the Faraday rotating medium and the synchrotron-emitting plasma
of the persistent source are nonetheless co-located. We apply these constraints
to proposed models for persistent source and Faraday screen associated with FRB
121102.
The extreme, time-variable Faraday rotation observed in the repeating fast
radio burst (FRB) 121102 demonstrates that some FRBs originate in dense and
dynamic magneto-ionic environments. Here we show that besides rotation of the
linear-polarisation vector (Faraday rotation), such media will generally
convert linear to circular polarisation (Faraday conversion). We use the
stringent constraints on circularly polarised emission in bursts from FRB
121102 to conclude the following. (i) All one-zone models where the persistent
radio source associated with FRB 121102 and the Faraday rotation are generated
by the same relativistic plasma are ruled out. (ii) The Faraday rotation must
occur in non-relativistic plasma where the characteristic magnetic field, $B$,
is determined to within a factor of order unity: $10,{rm mG}lesssim B
lesssim 30,{rm mG}$. (iii) The value of $B$ is close to the equipartition
magnetic field of the persistent radio source associated with FRB 121102,
suggesting that the Faraday rotating medium and the synchrotron-emitting plasma
of the persistent source are nonetheless co-located. We apply these constraints
to proposed models for persistent source and Faraday screen associated with FRB
121102.
http://arxiv.org/icons/sfx.gif
