Abstract: ABSTRACT Linear polarization has been measured in several gamma-ray burst (GRB) afterglows. After a few days, polarization arises from the forward shock emission that depends on the post-shock magnetic field. The latter can originate both from compression of existing fields, here the interstellar medium (ISM) magnetic field, and from shock-generated instabilities. For short GRBs, previous modelling of the polarization arising from the forward shock considered a random field fully or partially confined to the shock plane. However, the ISM magnet...
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