Search for Lorentz Invariance Violation from stacked Gamma-Ray Burst spectral lag data

TL;DR

This study stacked spectral lag data from 37 GRBs to test for Lorentz invariance violation, finding no decisive evidence under some models but indications under others, and highlighting the need for improved models of intrinsic spectral lags.

Contribution

It introduces a comprehensive stacking and Bayesian analysis approach to test LIV using GRB spectral lag data, revealing model-dependent evidence and the necessity for better intrinsic lag models.

Findings

No decisive evidence for LIV with constant intrinsic lag and unknown scatter.

Decisive evidence for LIV when using GRB-dependent intrinsic parameters.

Current models do not fit the spectral lag data well, indicating missing physics.

Abstract

A number of works have claimed detections of a turn-over in the spectral lag data for individual Gamma-Ray Bursts (GRBs), caused by an energy-dependent speed of light, which could be a possible manifestation of Lorentz invariance violation (LIV). Here, we stack the spectral lag data from a total of 37 GRBs (with a total of 91 measurements), to verify if the combined data is consistent with a unified model consisting of intrinsic astrophysical emission, along with another contribution due to LIV. We then carry out Bayesian model comparison to ascertain if this combined spectral lag data shows a preference for an energy-dependent speed of light, as compared to only an intrinsic astrophysical emission mechanism. We do not find a decisive evidence for such an energy-dependent speed of light for two different models of LIV. When we assume a constant intrinsic lag coupled with an unknown intrinsic scatter, we do not find any evidence for LIV. However, when we use GRB-dependent parameters to model the intrinsic emission, we get decisive evidence for LIV violation. We then carry out a search for LIV Standard Model Extension using this dataset as well as an independent search using a separate dataset consisting of rest-frame spectral lags. Finally, none of the models considered here with any of the aforementioned assumptions provide a good fit to the stacked spectral lag data, indicating that there is still missing Physics in the model for intrinsic spectral lags.