Energy dependent time delays induced by Lorentz Invariance Violation: discriminating source-intrinsic effects with blazar modeling and preparation of population studies with H.E.S.S. MAGIC and VERITAS.

Overview & Synopsis

Some models of quantum gravity, aiming at unifying general relativity and quantum mechanics, predict a Lorentz invariance violation (LIV) at Planck energy, expected to induce an energy-dependent velocity of photons in vacuum. One way to probe LIV is to look for energy-dependent time delays in the TeV gamma-ray signal coming from remote and variable cosmic sources such as active galactic nuclei, gamma-ray bursts and pulsars. However, time delays can also be generated from sources' radiative processes which are yet to be discriminated from LIV propagation effects. This distinction should be possible through the modelisation of sources emission mechanisms. This manuscript presents a time dependent leptonic model of blazar flares, and reviews the study of intrinsic time delays and their properties. Strong correlation and symmetry between time delays in the X-ray and gamma-ray domains are highlighted, which can be used to discriminate intrinsic from propagation effects. Contrary to LIV effects, intrinsic delays should not directly depend on the source distance. It should also be possible to separate both effects through population studies. A consortium between H.E.S.S., MAGIC and VERITAS experiments has been created to enlarge the catalog of usable datasets and combine them in a multi-source analysis. An advanced analysis software has been developed to test and calibrate a new standardised combination method, which is found to yield strong and robust constraints on the quantum gravity energy scale.