Separating source-intrinsic and Lorentz invariance violation induced delays in the very high energy emission of blazar flares

TL;DR

This study investigates methods to distinguish between intrinsic delays in blazar flares and delays caused by potential Lorentz invariance violation (LIV) at high energies, using simulations and observational diagnostics.

Contribution

It introduces new techniques to separate intrinsic and LIV-induced delays in blazar emissions, enhancing the ability to detect fundamental physics effects.

Findings

LIV effects can reduce correlation between X-ray and VHE gamma-ray emissions.

Euclidean distance from simultaneous X-ray and gamma-ray monitoring indicates LIV influence.

VHE hysteresis patterns are significantly altered by LIV effects.

Abstract

Aims: The aim of the present study is to explore how to disentangle energy-dependent time delays due to a possible Lorentz invariance violation (LIV) at Planck scale from intrinsic delays expected in standard blazar flares. Methods: We first characterise intrinsic time delays in BL Lacs and Flat Spectrum Radio Quasars in standard one-zone time-dependent synchrotron self-Compton or external Compton models, during flares produced by particle acceleration and cooling processes. We simulate families of flares with both intrinsic and external LIV-induced energy-dependent delays. Discrimination between intrinsic and LIV delays is then investigated in two different ways. A technique based on Euclidean distance calculation between delays obtained in the synchrotron and in the inverse-Compton spectral bumps is used to assess their degree of correlation. A complementary study is performed using spectral hardness versus intensity diagrams in both energy ranges. Results: We show that the presence of non-negligible LIV effects, which essentially act only at very high energies (VHE), can drastically reduce the strong correlation expected between the X-ray and the VHE gamma-ray emission in leptonic scenarios. The LIV phenomenon can then be hinted at measuring the Euclidean distance $d_{E}$ from simultaneous X-ray and gamma-ray flare monitoring. Large values of minimal distance $d_{E,min}$ would directly indicate the influence of non-intrinsic time delays possibly due to LIV in SSC flares. LIV effects can also significantly modify the VHE hysteresis patterns in hardness-intensity diagrams and even change their direction of rotation as compared to the X-ray behaviour. Both observables could be used to discriminate between LIV and intrinsic delays, provided high quality flare observations are available.