# Constraining Anisotropic Lorentz Violation via the Spectral-Lag Transition of GRB 160625B

## TL;DR

This paper uses the spectral-lag transition in GRB 160625B to set new constraints on anisotropic Lorentz violation, including bounds on high-dimension operators, by analyzing energy-dependent photon arrival times.

## Contribution

It introduces a novel method leveraging the spectral-lag transition in a unique gamma-ray burst to constrain direction-dependent Lorentz-violating effects, including high-dimension operators.

## Key findings

- Placed robust two-sided constraints on Lorentz-violating coefficients.
- Provided first bounds on effects from operators of mass dimension ten.
- Utilized the spectral-lag transition to distinguish Lorentz violation from source effects.

## Abstract

Violations of Lorentz invariance can lead to an energy-dependent vacuum dispersion of light, which results in arrival-time differences of photons arising with different energies from a given transient source. In this work, direction-dependent dispersion constraints are obtained on nonbirefringent Lorentz-violating effects, using the observed spectral lags of the gamma-ray burst GRB 160625B. This burst has unusually large high-energy photon statistics, so we can obtain constraints from the true spectral time lags of bunches of high-energy photons rather than from the rough time lag of a single highest-energy photon. Also, GRB 160625B is the only burst to date having a well-defined transition from positive lags to negative lags, which provides a unique opportunity to distinguish Lorentz-violating effects from any source-intrinsic time lag in the emission of photons of different energy bands. Our results place comparatively robust two-sided constraints on a variety of isotropic and anisotropic coefficients for Lorentz violation, including first bounds on Lorentz-violating effects from operators of mass dimension ten in the photon sector.