A polarized gamma ray emission spread over a sufficiently wide energy band
from a strongly magnetized astrophysical object like gamma ray bursts (GRBs)
offers an opportunity to test the hypothesis of axion like particles (ALPs).
Based on evidences of polarized gamma ray emission detected in several gamma
ray bursts we estimated the level of ALPs induced dichroism, which could take
place in the magnetized fireball environment of a GRB. This allows to estimate
the sensitivity of polarization measurements of GRBs to the ALP-photon
coupling. This sensitivity \gag\le 2.2\cdot 10^{-11} {\rm GeV^{-1}}
calculated for the ALP mass ma=10−3eV and MeV energy spread of
gamma ray emission is competitive with the sensitivity of CAST and becomes even
stronger for lower ALPs masses.Comment: Contribution to Proc. 4th Patras Workshop on Axions, WIMPs and WISPs
(18-21 June 2008, DESY
