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

TL;DR

This study investigates whether the speed of light varies with photon energy by analyzing a high-energy flare from galaxy PKS 2155-304, finding no significant time lag and setting limits on quantum gravity theories.

Contribution

It provides the first observational constraints on energy-dependent speed of light using VHE gamma-ray data from PKS 2155-304.

Findings

No significant energy-dependent time lag detected

Lower limits established on quantum gravity energy scale

Constraints improve previous bounds on speed of light modifications

Abstract

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. Since no significant time lag is found, lower limits on the energy scale of speed of light modifications are derived.