I read recently that the MAGIC telescope in Las Palmas detected a 4min divergence between photons of high and lower energy, which were traveling from galaxy Markarian 501. They say that the measurement is pretty accurate and it only remains to be re-confirmed. An old paper from J.Ellis, D. Nanopoulos & N.Mavromatos arises on the surface now, were it is suggested that the speed of light is not constant, but depends on the photon's frequency. Could someone pinpoint me a paper or something for more details? What does the rest of the community say about these claims?