Polarization Measurements as a Probe of Axion-Photon Coupling: a Study of GRB 221009A

Axion Like Particles (ALPs) can be produced in Gamma Ray Bursts, altering the polarization of the electromagnetic emission in these events. For the first time, we derive bounds on the axion-photon coupling from polarization measurements of GRB 221009A, performing a full calculation of the Stokes parameters, as it is typically done in the astrophysics community. Within astrophysical uncertainties, our limits on the axion-photon coupling are competitive with complementary probes in the axion mass range 10^-9 eV ≲ m_a ≲ 10^-8 eV, further allowing to probe motivated parameter space of ALP dark matter.