Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-07-26
MNRAS, 394, L21 (2009)
Astronomy and Astrophysics
Astrophysics
MNRAS Letters, in press
Scientific paper
10.1111/j.1745-3933.2008.00602.x
Recent findings by gamma-ray Cherenkov telescopes suggest a higher transparency of the Universe to very-high-energy (VHE) photons than expected from current models of the Extragalactic Background Light. It has been shown that such transparency can be naturally explained by the DARMA scenario, in which the photon mixes with a new, very light, axion-like particle predicted by many extensions of the Standard Model of elementary particles. We discuss the implications of DARMA for the VHE gamma-ray spectra of blazars, and show that it successfully accounts for the observed correlation between spectral slope and redshift by adopting for far-away sources the same emission spectrum characteristic of nearby ones. DARMA also predicts the observed blazar spectral index to become asymptotically independent of redshift for far-away sources. Our prediction can be tested with the satellite-borne Fermi/LAT detector as well as with the ground-based Cherenkov telescopes HESS, MAGIC, CANGAROOIII, VERITAS and the Extensive Air Shower arrays ARGO-YBJ and MILAGRO.
Angelis Alessando de
Mansutti Oriana
Persic Massimo
Roncadelli Marco
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