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

MAGIC Collaboration; Albert, J.; Aliu, E.; Anderhub, H.; Antonelli, L. A.; Antoranz, P.; Backes, M.; Baixeras, C.; Barrio, J. A.; Bartko, H. et al.
Bibliographical reference

Physics Letters B, Volume 668, Issue 4, p. 253-257.

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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 ≃1+E, n=1,2. Parametrizing the delay between γ-rays of different energies as Δt=±τE or Δt=±τE, we find τ=(0.030±0.012) s/GeV at the 2.5-σ level, and τ=(3.71±2.57)×10 s/GeV, respectively. We use these results to establish lower limits M>0.21×10 GeV and M>0.26×10 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.
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The MAGIC Collaboration is integrated by 20 research institutes and university departments from Armenia, Bulgaria, Finland, Germany, Italy, Poland, Spain, Switzerland and USA. The collaboration comprises two 17m diameter telescopes, located at the Roque de los Muchachos Observatory, designed to measure the Cherenkov radiation associated with

García López