GRB 210619B optical afterglow polarization

We observed the optical afterglow of the long gamma-ray burst GRB210619B using optical polarimetry, in the time frame 5967-8245 seconds after the burst. We detected a 5 σ significant polarization P = 1.5 ± 0.3 % with a polarization angle EVPA = 8 ± 6 o. The polarization remained constant throughout our observations and is likely intrinsic to the GRB afterglow.