Limits on an Energy Dependence of the Speed of Light from a Flare of the Active Galaxy PKS 2155-304

Understand

In the past few decades, several models have predicted an energy-dependence of the speed of light in the context of quantum gravity.

• For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags.
• In this paper a search for such time lags during the H.E.S.S.
• observations of the exceptional very high energy flare of the active galaxy PKS 2155-304 on 28 July in 2006 is presented.