Sensitivity of Astrophysical Observations to Gravity-Induced Wave   Dispersion in Vacuo
  We discuss possible signatures of quantum gravity for the propagation of light, including an energy-dependent velocity (refractive index), dispersion in velocity at a given energy, and birefringence. We also compare the sensitivities of different astrophysical observations, including BATSE data on GRB 920229, BeppoSAX data on GRB 980425, the possible HEGRA observation of GRB 920925c, and Whipple observations of the active galaxy Mrk 421. Finally, we discuss the prospective sensitivities of AMS and GLAST. 
G. Amelino-Camelia, John Ellis, N.E. Mavromatos, D.V. Nanopoulos and   Subir Sarkar