Constraints on Lorentz Invariance Violation using INTEGRAL/IBIS   observations of GRB041219A
  One of the experimental tests of Lorentz invariance violation is to measure the helicity dependence of the propagation velocity of photons originating in distant cosmological obejcts. Using a recent determination of the distance of the Gamma-Ray Burst GRB 041219A, for which a high degree of polarization is observed in the prompt emission, we are able to improve by 4 orders of magnitude the existing constraint on Lorentz invariance violation, arising from the phenomenon of vacuum birefringence. 
P. Laurent, D. Gotz, P. Binetruy, S. Covino, A. Fernandez-Soto
astro-ph.HE gr-qc