  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 invisible axion. The axionic
induced dichroism of gamma rays at different energies should cause a
misalignment of the polarization plane for higher energy events relative to
that one for lower energies events resulting in the loss of statistics needed
to form a pattern of the polarization signal to be recognized in a detector.
According to this, any evidence of polarized gamma rays coming from an object
with extended magnetic field could be interpreted as a constraint on the
existence of the invisible axion for a certain parameter range. Based on
reports of polarized MeV emission detected in several GRBs we derive a
constraint on the axion-photon coupling. This constraint $\g_{a\gamma\gamma}\le
2.2\cdot 10^{-11} {\rm GeV^{-1}}$ calculated for the axion mass $m_a=10^{-3}
{\rm eV}$ is competitive with the sensitivity of CAST and becomes even stronger
for lower masses.
