Multi-Waveband Synchrotron Polarization of Gamma-Ray Burst Afterglows. (arXiv:2005.03710v2 [astro-ph.HE] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Shimoda_J/0/1/0/all/0/1">Jiro Shimoda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Toma_K/0/1/0/all/0/1">Kenji Toma</a>
Multi-waveband synchrotron linear polarization of gamma-ray burst (GRB)
afterglows is studied under the assumption of anisotropic turbulent magnetic
field with coherence length on plasma skin depth scales in the downstream of
forward shocks. We find that for typical GRBs, in comparison to the optical
polarization, the radio polarization degree shows a similar temporal evolution
but a smaller peak value by a factor of ~ 5. This results from differences of
observed intensity image shapes between the radio and optical bands. We also
show that the polarization degree spectrum has a gradual variation from low to
high polarization regime above the intensity spectral peak frequency, and that
the difference of polarization angles in the two regimes is zero or 90 degrees.
Thus, simultaneous multi-waveband polarimetric observations of GRB afterglows
would be a new firm test of the plasma-scale magnetic field model. We also
discuss theoretical implications from the recent detection of radio linear
polarization in GRB 171205A with ALMA, other models of magnetic field
configuration, and Faraday depolarization effects by thermal electrons.
Multi-waveband synchrotron linear polarization of gamma-ray burst (GRB)
afterglows is studied under the assumption of anisotropic turbulent magnetic
field with coherence length on plasma skin depth scales in the downstream of
forward shocks. We find that for typical GRBs, in comparison to the optical
polarization, the radio polarization degree shows a similar temporal evolution
but a smaller peak value by a factor of ~ 5. This results from differences of
observed intensity image shapes between the radio and optical bands. We also
show that the polarization degree spectrum has a gradual variation from low to
high polarization regime above the intensity spectral peak frequency, and that
the difference of polarization angles in the two regimes is zero or 90 degrees.
Thus, simultaneous multi-waveband polarimetric observations of GRB afterglows
would be a new firm test of the plasma-scale magnetic field model. We also
discuss theoretical implications from the recent detection of radio linear
polarization in GRB 171205A with ALMA, other models of magnetic field
configuration, and Faraday depolarization effects by thermal electrons.
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