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oai:docta.ucm.es:20.500.14352/508082024-09-06T16:25:18Zcom_20.500.14352_14col_20.500.14352_15

00925njm 22002777a 4500 dc Antoranz Canales, Pedro author Barrio Uña, Juan Abel author Contreras González, José Luis author Fonseca González, María Victoria author Miranda Pantoja, José Miguel author Nieto Castaño, Daniel author 2008-10-16 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 similar or equal to 1 + (E/M-QGn)(n), n = 1, 2. Parametrizing the delay between gamma-rays of different energies as Delta t = +/-tau E-1 or Delta t = +/-tau E-q(2), we find tau(1) = (0.030 +/- 0.012) s/GeV at the 2.5-sigma level, and tau(q) = (3.71 +/- 2.57) x 10(-6) s/GeV2, respectively. We use these results to establish lower limits M-QG1 > 0.21 X 10(18) GeV and M-QG2 > 0.26 x 10(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. (C) 2008 Elsevier B.V. All rights reserved. 0370-2693 10.1016/j.physletb.2008.08.053 https://hdl.handle.net/20.500.14352/50808 http://dx.doi.org/10.1016/j.physletb.2008.08.053 http://www.sciencedirect.com http://arxiv.org/abs/0708.2889 Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope