Is there any evidence for extra-dimensions or quantum gravity effects   from the delayed MeV-GeV photons in GRB 940217?
  The discovery of X-ray afterglows of GRBs, and the identification of host galaxies of GRBs, confirm the cosmological origin of GRBs. However, the discovery of the delayed MeV-GeV photons in GRB940217 imposes serious challenges for the standard emission model of GRB. Although the delayed MeV-GeV photons might be explained by some radiation emission mechanisms, the mystery of detecting an 18 GeV photon still remains unsolved. We suggest that the detection of the 18-GeV photon $ \sim $4500 s after the keV/MeV burst in GRB 940217 provides a strong evidence for the existence of extra-dimensions and/or quantum gravity effects. The delay scale of the 18-GeV photon leads to an estimation of the fundamental energy scale, associated with the linear energy dependence of the speed of light, of the order of $2.1\times 10^{15}$ GeV, which is consistent with the results obtained by another independent analysis on the data of OSSE and BATSE. 
K. S. Cheng, T. Harko