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Abstract: As very high energy ~100 GeV gamma rays travel over cosmological distances,their flux is attenuated through interactions with the extragalactic backgroundlight. Observations of distant gamma ray sources at energies between ~200 GeVand a few TeV by ground-based gamma ray telescopes such as HESS, however,suggest that the universe is more transparent to very high energy photons thanhad been anticipated. One possible explanation for this is the existence ofaxion-like-particles ALPs which gamma rays can efficiently oscillate into,enabling them to travel cosmological distances without attenuation. In thisarticle, we use data from the Fermi Gamma Ray Space Telescope to calculate thespectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186and H2356-309 at z=0.165, and use this in conjunction with the measurements ofground-based telescopes to test the ALP hypothesis. We find that theobservations can be well-fit by an intrinsic power-law source spectrum withindices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and thatno ALPs or other exotic physics is necessary to explain the observed degree ofattenuation.



Autor: Alexander V. Belikov, Lisa Goodenough, Dan Hooper

Fuente: https://arxiv.org/







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