Stringent Tests of Lorentz Invariance Violation from LHAASO Observations of GRB 221009A

TL;DR

The paper probes possible Lorentz invariance violation by testing energy-dependent photon propagation using the exceptionally rich TeV photon data from GRB 221009A detected by LHAASO. By applying two independent analyses—cross-correlation function and maximum-likelihood—while accounting for spectral evolution, energy dispersion, and EBL attenuation, the authors extract or constrain LIV-induced arrival-time delays. They report 95% CL lower limits on the linear and quadratic LIV scales, with $E_{ m QG,1} > 1.0\times10^{20}$ GeV (sub-luminal) or $>1.1\times10^{20}$ GeV (superluminal) and $E_{ m QG,2} > 6.9\times10^{11}$ GeV (sub-luminal) or $>7.0\times10^{11}$ GeV (superluminal), representing the strongest time-of-flight LIV bounds to date for the quadratic term and competitive limits for the linear term. The results demonstrate the robustness of LIV constraints against method biases and model uncertainties, driven by the unprecedented TeV-statistics of GRB 221009A and the careful calibration against biases. The work underscores the utility of very-high-energy GRB observations for constraining fundamental physics and highlights the potential gains from future VHE prompt-emission measurements.

Abstract

On October 9, 2022, the Large High Altitude Air Shower Observatory (LHAASO) reported the observation of the very early TeV afterglow of the brightest-of-all-time GRB 221009A, recording the highest photon statistics in the TeV band ever from a gamma-ray burst. We use this unique observation to place stringent constraints on an energy dependence of the speed of light in vacuum, a manifestation of Lorentz invariance violation (LIV) predicted by some quantum gravity (QG) theories. Our results show that the 95% confidence level lower limits on the QG energy scales are $E_{\mathrm{QG},1}>10$ times of the Planck energy $E_\mathrm{Pl}$ for the linear, and $E_{\mathrm{QG},2}>6\times10^{-8}E_\mathrm{Pl}$ for the quadratic LIV effects, respectively. Our limits on the quadratic LIV case improve previous best bounds by factors of 5--7.

Figures (7)

• Figure 1: Count rate light curves of GRB 221009A, as detected by LHAASO-WCDA, presented in ten $N_{\rm hit}$ segments. The time binning of the light curves used for analysis is 0.1 s; however, they are depicted here with 2 s intervals for clarity. The blue-marked range 232--400 s after the GBM trigger $T_0$ is selected for calculating the time lags.
• Figure 2: Relationship between the induced LIV value of $\overline{\eta_n}$ (with $\overline{\eta_1}$ in the left panel and $\overline{\eta_2}$ in the right panel) and the input $\eta_n$ (denoted as $\eta_1$ and $\eta_2$ respectively), obtained through a simulation procedure.
• Figure 3: $\chi^2$ as a function of the dimensionless LIV parameter $\eta_{n}$ for the linear case (on the left) and the quadratic case (on the right), utilizing the CCF method. The vertical dashed lines indicate the best fits, and the shaded areas represent the 95% confidence intervals.
• Figure 4: Distribution of best-fit values of $\eta_n$ from the shuffled data, presented for both linear (on the left) and quadratic (on the right) cases. The vertical lines indicate the means.
• Figure 5: Profile likelihood distributions resulting from the analysis with the ML method, depicted for both linear (on the left) and quadratic (on the right) cases. The vertical dashed lines signify the best fits after bias subtraction, and the shaded areas correspond to the 95% confidence intervals.