A relativistic electron-positron beam propagating through a magnetized electron-ion plasma is shown to generate both circularly and linearly polarized synchrotron radiation .
The degrees of circular and linear polarizations depend both on the density ratio of pair beam to background plasma and initial magnetization , and a maximum degree of circular polarization \langle P _ { \textrm { circ } } \rangle \approx 18 \% is found to occur for a tenuous pair beam .
We demonstrate that the generation of circularly polarized radiation is intrinsically linked to asymmetric energy dissipation of the pair beam during the filamentation instability dynamics in the electron-ion plasma .
These results can help in understanding the recent observations of circularly polarized radiation from gamma-ray-bursts .