Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope

TL;DR

This study analyzes gamma-ray photon timing from a galactic nucleus flare to test quantum gravity models, setting lower bounds on quantum gravity energy scales based on observed photon delays.

Contribution

It provides the first observational constraints on quantum gravity energy scales using gamma-ray timing from active galactic nuclei flares.

Findings

Lower limit on quantum gravity scale M_{QG1} > 0.21×10^{18} GeV

Lower limit on quantum gravity scale M_{QG2} > 0.26×10^{11} GeV

MAGIC telescope sensitivity confirmed through Monte Carlo simulations

Abstract

We analyze the timing of photons observed by the MAGIC telescope during a flare of the active galactic nucleus Mkn 501 for a possible correlation with energy, as suggested by some models of quantum gravity (QG), which predict a vacuum refractive index \simeq 1 + (E/M_{QGn})^n, n = 1,2. Parametrizing the delay between gamma-rays of different energies as \Delta t =\pm\tau_l E or \Delta t =\pm\tau_q E^2, we find \tau_l=(0.030\pm0.012) s/GeV at the 2.5-sigma level, and \tau_q=(3.71\pm2.57)x10^{-6} s/GeV^2, respectively. We use these results to establish lower limits M_{QG1} > 0.21x10^{18} GeV and M_{QG2} > 0.26x10^{11} GeV at the 95% C.L. Monte Carlo studies confirm the MAGIC sensitivity to propagation effects at these levels. Thermal plasma effects in the source are negligible, but we cannot exclude the importance of some other source effect.