Using recent polarimetric observations of the Crab Nebula in the hard X-ray band by INTEGRAL, we show that the absence of vacuum birefringence effects constrains O(E/M) Lorentz violation in QED to the level |\xi| < 9x10^{-10} at three sigma CL, tightening by more than three orders of magnitude previous constraints. We show that planned X-ray polarimeters have the potential the potential to probe |\xi|~ 10^{-16} by detecting polarization in active galaxies at red-shift ~1.
@article{arxiv.0809.0220,
title = {Gamma-ray polarization constraints on Planck scale violations of special relativity},
author = {Luca Maccione and Stefano Liberati and Annalisa Celotti and John G. Kirk and Pietro Ubertini},
journal= {arXiv preprint arXiv:0809.0220},
year = {2010}
}