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Title: On detecting oscillations of gamma rays into axion-like particles in turbulent and coherent magnetic fields

Background radiation fields pervade the Universe, and above a certain energy any γ-ray flux emitted by an extragalactic source should be attenuated due to e{sup +}e{sup -} pair production. The opacity could be alleviated if photons oscillated into hypothetical axion-like particles (ALPs) in ambient magnetic fields, leading to a γ-ray excess especially at high optical depths that could be detected with imaging air Cherenkov telescopes (IACTs). Here, we introduce a method to search for such a signal in γ-ray data and to estimate sensitivities for future observations. Different magnetic fields close to the γ-ray source are taken into account in which photons can convert into ALPs that then propagate unimpeded over cosmological distances until they re-convert in the magnetic field of the Milky Way. Specifically, we consider the coherent field at parsec scales in a blazar jet as well as the turbulent field inside a galaxy cluster. For the latter, we explicitly derive the transversal components of a magnetic field with gaussian turbulence which are responsible for the photon-ALP mixing. To illustrate the method, we apply it to a mock IACT array with characteristics similar to the Cherekov Telescope Array and investigate the dependence of the sensitivity to detect amore » γ-ray excess on the magnetic-field parameters.« less
Authors:
;  [1] ;  [2]
  1. The Oskar Klein Center for CosmoParticle Physics, Department of Physics, Stockholm University, Albanova, SE-10691 Stockholm (Sweden)
  2. Dipartimento di Matematica e Fisica ''Ennio De Giorgi'', Università del Salento and INFN—Sezione di Lecce, Via Arnesano, I-73100 Lecce (Italy)
Publication Date:
OSTI Identifier:
22375902
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2014; Journal Issue: 09; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BACKGROUND RADIATION; DISTANCE; ELECTRONS; GALAXY CLUSTERS; GAMMA RADIATION; MAGNETIC FIELDS; MILKY WAY; PAIR PRODUCTION; PHOTONS; POSITRONS; TELESCOPES