Photon propagation and the VHE gamma-ray spectra of blazars: how transparent is really the Universe?
- ,
- ,
- M. Persic(,)
- Trieste Observ. and
- INFN, Trieste and
- Udine U.
5 pages
Published in:
- Mon.Not.Roy.Astron.Soc. 394 (2009) L21-L25
e-Print:
- 0807.4246 [astro-ph]
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Abstract: (arXiv)
Recent findings by Imaging Atmospheric Cherenkov Telescopes (IACTs) suggest a transparency of the Universe to Very-High-Energy (VHE) photons beyond expectations based on realistic models of the Extragalactic Background Light. It has recently been shown that such transparency can be naturally explained by the mixing between the photon and a new very light Axion-Like Particle (ALP) predicted by many extensions of the Standard Model of elementary particles (DARMA scenario). We discuss the implications of the DARMA scenario for the observed spectra of blazars detected in the VHE band. In fact, contemplating all such blazars at once allows us to correlate the emitted and observed spectral indexes. Besides confirming the DARMA scenario in more general terms, we show that this picture automatically explains why - even starting from the same nominal value of 2.4 for the spectral index of all VHE blazars at emission - the observed spectral index predicted by the DARMA scenario reproduces the observations, becoming asymptotically independent of the source redshift, z, for large z. Our prediction can be tested in the near future by the satellite-borne GLAST detector as well as by the ground-based IACTs (H.E.S.S., MAGIC, CANGAROO III, VERITAS) and by the Extensive Air Shower arrays ARGO-YBJ and MILAGRO.- intergalactic radiation
- gamma-rays
- gamma ray: cosmic radiation
- blazar: spectrum
- gamma ray: UHE
- gamma ray: flux
- photon: transparency
- redshift: dependence
- axion
- photon axion: oscillation
References(44)
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