Limits on an energy dependence of the speed of light from a flare of the active galaxy PKS 2155-304 - Aharonian, F.; Akhperjanian, A.; Barres de Almeida, U.; Bazer-Bachi, A.; Becherini, Y.; Behera, B.; Beilicke, M.; Benbow, W.; Bernlöhr, K.; Boisson, C.; Bochow, A.; Borrel, V.; et al. (The American Physical Society, 2008)