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- Meyer, Manuel, et al.
(author)
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On detecting oscillations of gamma rays into axion-like particles in turbulent and coherent magnetic fields
- 2014
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In: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :9, s. 003-
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Journal article (peer-reviewed)abstract
- Background radiation fields pervade the Universe, and above a certain energy any gamma-ray flux emitted by an extragalactic source should be attenuated due to e(+)e(-) pair production. The opacity could be alleviated if photons oscillated into hypothetical axion-like particles (ALPs) in ambient magnetic fields, leading to a gamma-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 gamma-ray data and to estimate sensitivities for future observations. Different magnetic fields close to the gamma-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 photonALP mixing. To illustrate the method, we apply it to a mock TACT array with characteristics similar to the Cherekov Telescope Array and investigate the dependence of the sensitivity to detect a gamma-ray excess on the magnetic-field parameters.
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