Key points are not available for this paper at this time.
Explosive astrophysical events at high redshift can be used to place severe limits on the fractional variation in the speed of light with frequency (/c), the photon mass (m_), and the energy scale of quantum gravity (Eₐ₆). I find /c<6. 310^-21 based on the simultaneous arrival of a flare in GRB 930229 with a rise time of 22030 for photons of 30 and 200 keV. The limit on m_ is 4. 210^-44g for GRB 980703 from radio to gamma ray observations. The limit on Eₐ₆ is 8. 310^16GeV for GRB 930131 from 30 keV to 80 MeV photons.
Bradley E. Schaefer (Mon,) studied this question.