Constraining Lorentz invariance violation using the Crab Pulsar emission observed up to TeV energies by MAGIC

TL;DR

This study uses TeV gamma-ray observations of the Crab Pulsar to set new limits on Lorentz invariance violation, finding no significant energy-dependent time delays and constraining quantum gravity energy scales.

Contribution

It provides the first constraints on Lorentz invariance violation using Crab Pulsar data at TeV energies, improving previous bounds and analyzing systematic uncertainties.

Findings

No significant energy-dependent time delays observed.

Constraints on quantum gravity energy scales: >5.5×10^{17} GeV (linear), >5.9×10^{10} GeV (quadratic).

Systematic uncertainties increase the limits by 36-42%.

Abstract

Spontaneous breaking of Lorentz symmetry at energies on the order of the Planck energy or lower is predicted by many quantum gravity theories, implying non-trivial dispersion relations for the photon in vacuum. Consequently, gamma-rays of different energies, emitted simultaneously from astrophysical sources, could accumulate measurable differences in their time of flight until they reach the Earth. Such tests have been carried out in the past using fast variations of gamma-ray flux from pulsars, and more recently from active galactic nuclei and gamma-ray bursts. We present new constraints studying the gamma-ray emission of the galactic Crab Pulsar, recently observed up to TeV energies by the MAGIC collaboration. A profile likelihood analysis of pulsar events reconstructed for energies above 400GeV finds no significant variation in arrival time as their energy increases. Ninety-five percent~CL limits are obtained on the effective Lorentz invariance violating energy scale at the level of $E_{\mathrm{QG}_1} > 5.5\cdot 10^{17}$GeV ($4.5\cdot 10^{17}$GeV) for a linear, and $E_{\mathrm{QG}_2} > 5.9\cdot 10^{10}$GeV ($5.3\cdot 10^{10}$GeV) for a quadratic scenario, for the subluminal and the superluminal cases, respectively. A substantial part of this study is dedicated to calibration of the test statistic, with respect to bias and coverage properties. Moreover, the limits take into account systematic uncertainties, found to worsen the statistical limits by about 36--42\%. Our constraints would have resulted much more competitive if the intrinsic pulse shape of the pulsar between 200GeV and 400GeV was understood in sufficient detail and allowed inclusion of events well below 400GeV.